Until this wild week, which culminated Saturday with his being introduced as Joe Paterno's successor at scandal-scarred Penn State, the New England Patriots assistant was better known for his temperament than his talent.
Described by one friend as "fiercely intense but a guy you'd enjoy having a beer with," O'Brien famously engaged in a high-decibel dispute with Patriots quarterback Tom Brady in December, then delivered a war-dance of an address to his offensive line.
Those well-publicized tantrums have further inflamed the instant unhappiness his hiring engendered in Happy Valley.
Critics wondered why someone from the vast Nittany Lions family couldn't have been found and how a little-known aide from an NFL team whose better-known assistants have made spectacularly ineffective head coaches is going to shore up this badly damaged program.
But friends, former colleagues, and those who played for him contend O'Brien has been unfairly tarnished, especially for that spat with Brady.
"First of all, Tom Brady said afterward that he deserved it and that he respected Bill," said Phil Estes, a friend and former colleague who now is Brown's head coach. "Billy's a coach. A lot of people wouldn't have gone in there and tried to coach Tom Brady. They would just let him line up, do his thing, and win. Not Billy. He's coaching all the time. Tom Brady might know a lot of football, but Billy's going to coach him anyway."
Estes and others concede that while O'Brien might occasionally spill over the top, he's also an X's-and-O's genius who is never unprepared, comprehends football's complexities, and teaches them passionately. More significantly for this program fraught with doubts and troubles, he can be extremely persuasive.
"When Billy gets in front of that team, once they hear him and understand him, they will definitely walk away thinking 'This is the right guy,' " predicted Estes.
Until O'Brien has a record and a demeanor to dissect at Penn State, those NFL incidents and his lack of head-coaching experience will continue to define him. In the meantime, and for a long time, he will be compared to the 409-win legend he is replacing.
Like Paterno, O'Brien graduated from a Catholic prep school, then Ivy League Brown, and then became a college assistant.
But their biographical dissimilarities are just as apparent.
Paterno, for example, majored in literature at Brown, while O'Brien studied organizational behavior and management, skills that might be useful as he tries to push Penn State beyond the child-sexual-abuse scandal surrounding former assistant coach Jerry Sandusky that has overwhelmed the school.
The eldest of three children, Paterno was raised by first-generation Italian parents in cramped Brooklyn flats. O'Brien, the youngest of three brothers, grew up in tony Andover, his parents wealthy enough to afford a summer home on Cape Cod and a winter place in Florida.
If Paterno tended to whine his complaints, O'Brien screams them. If Paterno built his reputation on a coolheaded intellectualism, O'Brien's has been marked by visceral explosions. And while Paterno worked at one place for 61 years, O'Brien already has six teams on his resumé.
"Billy has great backbone," Estes said. "Billy is going to focus on the football part of it and not on who he's trying to follow, not on who he's trying to live up to. He's going to live up to just Billy O'Brien."
'Perfect for recruiting'
Bill O'Brien was born in Dorchester, Mass. His father, John, who made a fortune in the semiconductor industry, moved to Georgia for business in the 1970s. By 1977, when Bill was 8 years old, the O'Briens were back in Massachusetts.
The hypercompetitive youngster, who friends say inherited his mother's intensity, was a good athlete and better student.
He earned honors at exclusive St. John's Prep, a 95-year-old Xaverian Brothers school that occupies 175 leafy Massachusetts acres in Danvers.
After graduating in 1988, there was never any question where he was going to college. His father, Class of '55, and two brothers had played football at Brown.
O'Brien played mostly at linebacker and enhanced his growing reputation as someone who poured everything he had into the game. His coach, Mickey Kwiatkowski, described him as "the heart and soul" of the Bears.
"Bill is a leader in every sense of the word - physically and emotionally," Kwiatkowski said.
By the time O'Brien graduated in 1992, he knew he wanted to coach.
He taught the tight ends, then the linebackers as an unpaid Brown aide in 1993 and 1994. A year later, he moved to Georgia Tech as a graduate assistant under George O'Leary.
When Estes got the Brown job in 1998, his first hire was O'Brien, though their partnership proved short-lived.
"Billy and I had coached together at Brown," Estes said. "He was going to be my recruiting coordinator. He's got the perfect personality for recruiting. He has a great way of making kids feel good about themselves and the program."
Two months later, O'Leary called. He wanted O'Brien back in Atlanta, to be his running backs coach.
"George understood perfectly what he was losing, and I understood why he hired him back so quickly," Estes said.
Moving to offense
Though he had played mostly defense, O'Brien grew intrigued by the other side of the ball and in 2001 became O'Leary's offensive coordinator. A year later, he was named assistant head coach.
In 2001, Tech quarterback George Godsey set school records with 3,085 yards passing and 249 completions and completed 64.8 percent of his throws. In O'Brien's last two years at Georgia Tech, the Yellow Jackets averaged 26 points a game and compiled a 16-10 record.
"He's intense," said Joe Hamilton, the running backs coach at Georgia State, who had been a Tech quarterback under O'Brien and later coached with him at Maryland. "He's just so competitive. It's not unusual to see him firing teams up the way he did the offensive line of the Patriots. He's a guy that seeks perfection."
Apparently he didn't find it at Georgia Tech, because in 2003 he went to Maryland to join Ralph Friedgen, with whom he'd worked under O'Leary.
"I don't think he would have taken the [Penn State] job if he didn't think he could handle it," Friedgen told the Big Ten Network. "It isn't going to be easy. But he's a smart guy, and he's not going to get into something he doesn't think he can do."
In 2005, the peripatetic O'Brien went to Duke as offensive coordinator. Though the Blue Devils went 1-10 and 0-12 in his time there, his players insist O'Brien never changed.
"He's a really intense guy, and it was hard for him at Duke," said the Cleveland Browns' Thaddeus Lewis, his quarterback there. "You can't recruit all the guys you could at other schools, because of the academics. He had to deal with that.
"And going 0-12, for a coach to come in and stay as energetic and positive as he was, shows a lot about him. He could easily have shut it down like some of the kids probably shut it down. He stayed positive that whole season."
Always on the lookout for offensive-minded workaholics, Bill Belichick heard about O'Brien's mind-set and New England roots and offered him a job.
"I said to my wife, 'Colleen, this is something I can't pass up. I have an opportunity to work for Bill Belichick and this organization,' " O'Brien said in 2010. "And being from here played into it."
The job quickly became an obsession. The more time he spent in meetings, the less he was with his wife and two sons.
"What he is on the field is not the same guy that he is off the field," Estes said. "Billy's all about family. Any free time he gets he's going to be with them. But when he's coaching, he's all in. He wants perfection."
Despite all the success O'Brien's Patriots offenses have enjoyed, critics point to previously successful Belichick assistants who flopped when they ventured away from his system.
"People want to compare him to Romeo Crennel, Josh McDaniels, or Charlie Weis," Estes said. "Billy is not anything at all like them. Weiss, for example, has a huge ego. That's not Billy O'Brien at all. He's got a great [personality], a great sense of humor. I think Penn State is really going to enjoy him.
"Billy's just got to separate Jerry Sandusky from Penn State. And if anybody can do that, Billy can."
Big Ten Coaches' Salaries
Here is where Bill O'Brien's 2012 salary would fit into the 2011 list of Big Ten coaches in annual salary. For the 2012 list, Ohio State hired Urban Meyer, who will make $4 million to rank first, and Illinois hired Tim Beckman, who will make $1.6 million to rank seventh. O'Brien's No. 11 conference ranking is the same as the 2011 ranking of Joe Paterno, who earned $1.023 million.
RANK COACH SCHOOL 2011 SALARY
1. Kirk Ferentz Iowa $3.785 million
2. Brady Hoke Michigan $3.254 million
3. Bo Pelini Nebraska $2.775 million
4. Bret Bielema Wisconsin $2.6 million
5. Mark Dantonio Michigan State $1.918 million
6. Ron Zook* Illinois $1.755 million
7. Jerry Kill Minnesota $1.7 million
8. Kevin Wilson Indiana $1.26 million
9. Pat Fitzgerald Northwestern $1.19 million
10. Luke Fickell* Ohio State $1.172 million
11. Bill O'Brien Penn State $950,000
12. Danny Hope Purdue $925,000
* – No longer head coach at that school
Bill O'Brien's Contract Details
Bill O'Brien is set to earn about $2.5 million all told in 2012, his first year as Penn State head football coach. Here is how his earnings break down:
Base salary $950,000
Radio and TV $1 million
* – estimated
- Joe Juliano
More Coverage in Sports
O'Brien tries to win over former players and alumni. E1.
Phil Sheridan: Critics of the choice just don't get it. E1.
How Penn State found its coach. E9.
Larry Johnson will stay as defensive line coach. E9.
Contact staff writer Frank Fitzpatrick at 215-854-5068, email@example.com, or @philafitz on Twitter. Read his blog, "Giving 'Em Fitz," at www.philly.com/fitz