Behind Booker's polished national profile is Butler, the mayor's right-hand man and chief of staff, a behind-the-scenes guy who navigates the feudal world of Essex County politics - and the person who recently devised a controversial plan to install a Booker ally on a sharply divided City Council, triggering a near-riot.
Raised in Germantown and Mount Airy, schooled at Murrell Dobbins High School and Franklin and Marshall College, Butler, 39, has become Newark through-and-through. Or as PolitickerNJ.com put it in naming him to its "Power List" last month, he is "the mayor's City Hall eyes and ears" with his "hands on the controls of Booker's day-to-day operations."
Political watchers say that if Booker runs for governor - the mayor says he will make a decision by Christmas - Butler would be a key player in that race.
"If he'd want me to serve, I'd serve with him," Butler said in an interview in his large second-floor office in Newark's downtown City Hall.
Shortly after he said that, the mayor bounded into the office to declare that "Mo's the man" - even as he made fun of him for being too skinny.
Booker praised Butler's ability to drive the "massive transformation" of Newark amid staff cuts in City Hall and at the city's housing authority, where Butler is chairman.
"I get so much attention and very few people know who Mo is, but the reality is I wouldn't be doing the things I'm doing if it wasn't for Mo Butler," Booker said.
Bill Castner, a South Jersey Democratic politico, dealt with Butler during negotiations this year on the reorganization of the higher education system.
"When you deal with smart and influential staffers, the ultimate question is, 'Can they truly speak on behalf of their bosses?' " Castner said. "Obviously with Mo and Mayor Booker, that question isn't even debatable."
Butler graduated as a political science major wanting to do "good in the world." He then earned an master's degree at Rutgers University's Eagleton Institute of Politics and took a job doing workforce development in Paterson.
That was when a professor at Eagleton told him of Booker, then a twentysomething council member in Newark: "You need to get to know this guy."
So Butler invited Booker to speak at a graduation for the program he was running. "All of this was a charade for me to meet him," Butler said.
Booker pulled up in a beat-up Jeep Cherokee, and "he blew everyone away with his speech."
Butler loves cities - "I love corner stores, bodegas, I love the diversity, the rhythm of the city." But it was Booker who inspired Butler to choose Newark as his adopted home. He got a job running a youth development organization called Newark Do Something.
He fits the profile of those whom Booker has surrounded himself with - a best-and-brightest group, often from outside of Newark, with pedigrees in the nonprofit sector.
So when Booker started a new nonprofit in 2003 called Newark Now, he hired Butler to run it. Then in 2008, in his first term as mayor, Booker brought Butler on as chief of staff.
"The way it works is the mayor is the visionary, he's the aspirational leader, he sets the tone," Butler said. "It's my job to operationalize that."
The council controversy is a case in point. Realization of Booker's agenda depends on support from council, which is increasingly hostile to him and resentful of his national prominence. A recent vacancy meant whomever council appointed for the ninth member could swing votes.
Anti-Booker forces put up the son of Booker's predecessor, Sharpe James. The former mayor served time in prison for corruption.
"It's my job to make sure that doesn't happen," Butler said of losing the edge on council. So he pulled a card that had never been played - bringing the mayor into council last month to cast the deciding vote for a pro-Booker member. The meeting dissolved into chaos, with police pepper-spraying the crowd.
Another vote was held last week, and Booker again cast the deciding vote. But the move has been challenged in court; a judge will hear the case Tuesday.
Councilwoman Mildred Crump called the Butler-orchestrated move a "hostile takeover of municipal council." She did not return a call last week to talk more specifically about Butler's role.
Sharpe James, in an interview on NJTV, called it a "conspiracy," saying that "Mr. Modia Butler," Booker, and others were involved in a "clandestine move in order to name their candidate."
Booker's treatment at the council meetings stood in stark contrast to the way he is fawned over by national media. One council member yelled "Shame on you!" at Booker as he walked out of the chambers, head bowed.
"Mo's role is complicated by the kind of mayor he works for," said Clement A. Price, a historian at Rutgers-Newark.
Booker has "interests and ambitions that take him beyond Newark," Price said, so "Mo has the added responsibility of looking after Booker's profile and national stature and reputation - as well as maintaining his stature in the city of Newark."
Butler describes himself as "stern, up-front" in how he goes about his job. "I can cut through all their crap," Butler said of council members. "Because I know the backstory, I know who they are, I know who supports them."
Sans tie in a pinstripe suit, Butler appears laid back. But the head of the Newark Parking Authority, Ernest Booker (no relation to Cory), says: "Don't let that fool you."
The mayor said: "When the time comes to punch someone in the nose when it's necessary, even though he looks like a lightweight, he's Muhammad Ali."
A divorced father of a 9-year-old girl, Butler relaxes by DJing, for free, around town. "This job is difficult, bro," he said.
Part of the difficulty is that "the mayor moves fast." Still, Butler has stopped him long enough to give him advice about whether to run for governor.
What did he tell him?
With a smile, ever loyal, Butler says: "I'm not going to share."
Contact Matt Katz at 609-217-8355 or email@example.com, or follow on Twitter @mattkatz00. Read his blog, "Christie Chronicles," at www.philly.com/