Mr. Katz, 72, whose enormous wealth never obscured his devotion to the less fortunate or his love of the underdog, was killed on Saturday in a plane crash in Massachusetts.
Across the region, in Camden, where he built schools and Boys & Girls Clubs, to Philadelphia, where he bought and supported the major newspapers, to North Jersey, where he owned the basketball Nets and hockey Devils, staggered friends and family struggled to accept the news that he was gone.
Mr. Katz' reach, influence and ideas touched almost every sphere of local public life, from media, to law, to politics, to health care, to education and philanthropy. His death occurred four days after he and fellow investor H. F. "Gerry" Lenfest teamed to win a dramatic, climactic owners-versus-owners auction for control of The Inquirer, The Daily News and Philly.com, a victory that many believed had assured the future of Philadelphia journalism for years to come.
Smart, decisive, kind, loyal, savvy, creative, eccentric, empathic, inimitable, a brilliant advisor, the best friend, a fierce advocate - Mr. Katz embraced his wealth and the power that came with it, while at times seeming surprised and amused that a kid from Camden could walk with presidents.
"He would always ask, 'Did you ever think I would be so successful?' " his friend Robert Rovner recalled.
But Mr. Katz, people in big organizations said on Sunday, was not just someone who showed up with a check.
He became passionately involved in the issues he cared about, and had the ability to add real intellectual value and business acumen.
He never lost touch with his childhood friends. And at 72 he possessed the energy and drive of a much younger man, remaining trim and fit as the result of regular workouts with a personal trainer.
Decades after he played junior varsity basketball for the Camden High School Panthers, he remained a deadly free-thrown shooter. Two years ago, Mr. Katz beat Shaquille O'Neal in a free-throw contest at the Prudential Center in Newark. He also beat President Clinton in an impromptu game of one-on-one nerf basketball in Mayor Rendell's office.
"He was the most unique man I ever met," said Patrick O'Connor, chairman of the Temple Board of Trustees, who struggled to contain his grief. "Temple has lost their greatest alum."
Mr. Katz and his late wife, Marjorie, raised two children, Drew and Melissa. Mr. Katz' longtime companion, Nancy Phillips, is city editor of The Inquirer.
"My father was my best friend," Drew Katz said Sunday. "He taught me everything. He never forgot where and how he grew up, and he worked tirelessly to support his community in countless ways that were seen and unseen. ... But his greatest accomplishment by far was being the most amazing father to my sister and me, and grandparent to his four grandchildren."
For all the demands on his time, Mr. Katz never missed an event involving his grandchildren. They called him "Poppy," demanding he get down on the floor and play, or get into the pool, to which Mr. Katz happily obliged.
Drew Katz recalled how, when he was a boy, his father would bring him to his business office and solicit his advice. Mr. Katz was best man at his son's wedding. As father and son, and as grown men together, they would take long walks and talk of life, family and business.
Drew Katz, 42, recalled how when he was 9, his father and he sat together at the sixth game of the 1980 World Series. With two strikes on the Royals' Willie Wilson and the Phillies poised to win, the older man turned and said, "You're witnessing history, son."
Twenty-eight years later in 2008, father and son were in almost the exact same seats in a new stadium, and with two outs Mr. Katz turned to his now-grown child.
"Remember?" he said. "Remember?"
The son cut him off: "'You're witnessing history, son.'"
For all his wealth, Mr. Katz could be happily off-beat. The week before he and Lenfest bid $88 million to win The Inquirer, Mr. Katz strolled through the newsroom in jeans, a T-shirt, yellow-green neon sneakers and Dr. Dre Beats headphones.
He slapped reporter Dylan Purcell on the shoulders, then playfully stuck his headphones over the ears of reporter Susan Snyder. People in the newsroom thought Mr. Katz bore the look of someone who intended to bid - and to win.
Almost everyone in Philadelphia recognizes Mr. Katz' name from his service on prominent boards of universities and his huge donations - including $25 million to Temple in 2013. But they don't know how rare and unusual was his rise to the top, or how his energy might have gone in another direction.
He could easily have become a journalist.
As an undergraduate at Temple, he was asked to drive famed Washington columnist Drew Pearson back to the airport after the reporter spoke to students.
Pearson was so impressed that he offered Mr. Katz a job as a research assistant. And Mr. Katz, after a year by Pearson's side, came away immersed in the arts of journalism - and with the name he would later bestow on his son.
"Sometimes I see money in the hands of people who do nothing but evil and harm and I say, 'Why'd the Lord give that person money?'" former Gov. Rendell said on Sunday. "But the Lord got it right giving Lew his money."
Former President Clinton remembered a meeting at The Clinton Foundation in 2007 when, after hearing how tennis great Andre Agassi founded a school in the poorest neighborhood of Las Vegas, Mr. Katz immediately pledged to build a charter school in Camden - now the Katz Academy.
"It was just a spontaneous moment," Clinton said Sunday. "That guy did a lot with his heart."
Mr. Katz touched the lives of people he never met or knew. He was known for giving to his beloved Temple, but there are buildings across the Delaware Valley that were built by donations from Mr. Katz - of which he never said a word.
Only on Sunday, after his death, did friends tell stories of how he quietly wrote six-figure checks to build a playground or keep a Boys & Girls club from closing. He once anonymously paid for the funeral of a friend's parent, then refused to admit it or accept thanks.
He was never afraid to tell a friend, often another grown man, that he loved him. On Sunday, friend after friend said the same about him.
"Lewis was the epitome of the word 'mensch,'" said a devastated Ed Snider, chairman of Comcast Spectacor, which owns the Flyers. "He gave everything he had to make a difference."
Last month, when Temple announced it would name its medical school after Mr. Katz, he said his mother had wanted him to be a doctor - but he couldn't stand the sight of blood.
Instead, he became a lawyer and businessman, making millions in parking lots, billboards and sports.
Mr. Katz was a former owner of Kinney Parking Systems, at the time the largest parking company in New York City, and the former chairman of Interstate Outdoor Advertising, one of the largest regional outdoor-advertising firms in the country. He was the majority owner of five radio stations in Atlantic and Cape May counties at the Jersey shore, and a founding partner of the law firm Katz, Ettin & Levine in Cherry Hill.
He started with nothing. His father died when he was months old. All the father could afford to leave to Lewis was height - the son grew to 6-foot-2. Mr. Katz' mother worked two or three jobs at a time to put food on the table.
Mr. Katz grew up knowing what it meant to be poor, how it felt to need and not have. Those lean years in Camden marked him. All his life, he remained keenly sensitive to others who struggled to get by.
When as a teenager Temple offered him a scholarship, he grabbed it - arriving at the university scared and worried that he was out of his league. Instead, he excelled, going on to graduate first in his class from Dickinson Law School.
He would later tell friends that he loved Temple because it was the school for kids who, like him, desperately wanted to get an education, not a school for those headed to college because their parents decided they should go.
"Lew was like my brother," said Rovner, a former law partner who met Mr. Katz at Temple in 1961. "We were two poor kids who couldn't afford to be in a fraternity."
Even in their early law practice years, when they had an office at 15th and Locust, Mr. Katz was generous toward others. When they walked to lunch, he would regularly hand $10 or $20 to the homeless people they passed.
Rovner recalled that about eight years ago, they went with friends on a trip to Morocco. A strong supporter of Jewish causes, Mr. Katz wanted to learn more about the once thriving community in Morocco, and offer aid to the relatively few Jews who remained in the country.
Afterward, Rovner said, he was talking with the tour guide, who excitedly shared that someone had given her a $100 tip.
"We all knew," Rovner said, "it had to have been Lewis."
As Mr. Katz' success and wealth expanded, the gifts became larger.
In 2013, he made a $25 million gift to his beloved Temple, which in May announced that it would rename the medical school in his honor.
"I loved him," Temple's O'Connor said. "He was so different than other people I've met in my life. If I said, 'Lewis, I'm doing 'X' for a family or a charity, he'd want to help. You'd be reluctant to ask because he'd say yes to everything."
Mr. Katz was the director of the Katz Foundation, which supports multiple charitable, educational and medical causes. His $15 million gift to The Dickinson School of Law at Pennsylvania State University helped fund a law school building in State College that bears his name.
At Dickinson's original campus in Carlisle, a new addition to the law school is Lewis Katz Hall. He established an annual prize and endowed a visiting professorship in cardiovascular research at Columbia University, and served on the board of visitors of Columbia University Medical School.
Besides having owned the New Jersey Nets and New Jersey Devils, he served on the NBA's board of governors, and at the time of his death was a shareholder of the Nets, the New York Yankees and the YES Network. In all those ventures, Mr. Katz pledged a share of team profits to benefit inner-city youth.
NBA Commissioner Adam Silver mourned with others on Sunday.
"He was a visionary businessman," Silver said, noting that it was Mr. Katz who led the Nets to the 2002 and 2003 to the NBA Finals for the first time in franchise history.
In his hometown of Camden, among the nation's poorest cities, Mr. Katz established several programs to help children. He helped build two Boys & Girls Clubs that serve nearly 3,000 young people each year, and served on the board of governors for the Boys & Girls Clubs of America.
Mr. Katz was a founder of Katz Academy, the charter school in Camden that serves grades kindergarten through fourth grade. A second Katz Academy recently opened in the city's Cramer Hill section.
He helped fund a new home for Nazarene Baptist Church, whose leaders named him an honorary member even though he was Jewish. He supported the city's Catholic schools and provided scholarships for its students.
He helped build Jewish Community Centers in Cherry Hill and Margate, both of them named for his parents, and helped found a third, now under construction in Princeton, also named for parents. He was instrumental in establishing a Hebrew day school in Voorhees that's named for his children.
He served on the board of Dickinson Law School, of Temple University, of Temple Hospital University Health System, the Fox Chase Cancer Center, the Museum of the American Revolution, the Starlight Children's Foundation, and the National Constitution Center.
"Lewis had none of the normal attributes that you would associate with vastly successful people," said his attorney and friend of 30 years, Stephen Harmelin. He was warm, and to others could seem a little disorganized. "I called him 'The Scarlet Pimpernel" - a quick-thinking master of disguise in the book and play of the same name - "because he was here, there and everywhere."
People forget that Mr. Katz was a first-rate litigator, he said, a lawyer who was thorough and smart, and could see opportunities for action in a courtroom, a vision he would later exercise in business.
Of course no one owns major corporations or sports teams without being able to make decisions that impact the lives of others, sometimes painfully.
"He was never tough in the way that people use that word," Harmelin said. "I never once have seen him lose his temper."
Retired New Jersey Superior Court Judge Isaiah Steinberg recalled growing up with Mr. Katz in Camden, playing basketball together at the Jewish Center. As they aged, a gap grew between their incomes and lifestyles, but Mr. Katz remained loyal, Steinberg said. And not just to him, but to others he knew from the days when none of them had any money.
"He was still the guy from Langham Avenue," Steinberg said. "His friendships with so many people from high school and college lasted."
When Steinberg was invited to join Mr. Katz in the owners' box at a Nets game, Steinberg said, the intent always seemed to simply share the fun rather than show off. There was no denying Mr. Katz' ego contributed to his drive, he said, "but ego isn't always a bad thing."
Mr. Katz loved having the freedom to pick up and go anywhere he chose, when he wanted to go, and to bring along anyone he wished.
Several friends recalled being invited on the spur of the moment to fly with Mr. Katz to Mount Rushmore. Or to the Grand Canyon. Or to spend a night in New York. And if they had not packed a bag, he would pay for them to go out and buy a change of clothes for the next day.
Once, recalled former U.S. Rep. Marjorie Margolies, friends with Mr. Katz since her first political campaign, Mr. Katz called to say he wanted to bring more attention - and money - to presidential libraries.
In no time, she said, he had arranged a trip on his private plane to take several influential friends to visit the Eisenhower Library in Abilene, Kansas, where they received a personal tour by Julie and David Eisenhower.
"He was somebody who had an idea a minute," she said.
On Tuesday, hours after winning The Inquirer at auction, a battle many expected he would lose, Mr. Katz stood before relieved and grateful newspaper employees at 801 Market Street.
He refused to gloat, later telling reporters that both sides had won.
"One party got a wonderful return on his investment," Mr. Katz said, "and the other party has the privilege to give the newspaper . . . all it deserves."
Mr. Katz often said that one good thing about becoming involved in owning the The Inquirer - his 2012 partnership with George Norcross had soured into litigation - was he got to know and work with Lenfest.
"We had instant chemistry," a stricken Lenfest said on Sunday. "We both felt an obligation, almost a trust, to preserve the newspaper, and its history of great reporting and responsibility to the community."
On Sunday, as he thought of his friend, Lenfest said, "I feel Lewis' presence all around."
It was Lenfest and Mr. Katz who fought to win the court-ordered reinstatement of Inquirer Editor William K. Marimow, after publisher Robert Hall had fired him at Norcross' behest.
"He loved journalism," Marimow said on Sunday. "As an owner, he was delighted to be once again in journalism. He loved providing tips - but never nudged."
It's probably impossible to overstate Mr. Katz' quiet commitment to the community, Marimow said.
"When you go to Camden, to Cherry Hill, there are lots of places that bear Lewis' generosity," he said, "but they do not bear his name."
Newspaper Guild Executive Director Bill Ross - who had disagreements with Mr. Katz - called him "a real gentleman."
Ross grew up in New Jersey as a Nets and Devils fan, and watched on the day Mr. Katz appeared on TV, pumping his fist and shouting, "Yes! Yes!" as the Nets won the NBA draft lottery - a huge moment that enabled the team to claim Kenyon Martin.
"I don't feel like this is real today, I really don't," Ross said on Sunday.
He noted that people say grief is the price that's paid for having loved someone.
"We'll see that over the next weeks and months with Mr. Katz," Ross said. "He definitely loved a lot of people, and people loved him back."