Michael Sacks, the über-wealthy asset management CEO—and unpaid, largely unheralded adviser to his friend Rahm Emanuel—is so discreet and self-effacing, so spotlight averse, that coaxing him to describe mayoral interactions is not just like pulling teeth. It’s like executing a root canal.

“I don’t think it’s my place to speak publicly about private conversations,” says Sacks, 54. “It defeats the purpose of having private conversations and would prohibit me from being a confidant.”

No worries there. The GCM Grosvenor chairman and CEO has become Emanuel’s go-to adviser. The mayor named him vice chairman of the development group World Business Chicago and a member of his economic council. But those titles don’t begin to describe his outsize City Hall influence—one that has only grown over the past year as Emanuel faces more scrutiny.

“Rahm gives Michael assignments,” says their mutual friend David Axelrod—for example, the parking meter deal renegotiation in 2013, during which, Sacks told me, he persuaded company officials to provide “enhancements” such as pay-by-cell-phone capabilities and free Sundays. Alderman Scott Waguespack says Sacks was “front and center” in the effort to try to render the awful deal a bit less awful. “He plays a pretty substantive role in bigger issues and bigger projects,” Waguespack says. “He sits at the negotiating table with the businesses.”

In the wake of all the heat Emanuel took over his seemingly self-serving delayed release of the Laquan McDonald video, the mayor’s dependence on Sacks has become more pronounced. But with that, Sacks’s reputation seemed to singe at the edges as news surfaced that he was cc’ed in emails from the mayor’s office about the Chicago Police Department’s plans to spy on Black Lives Matter activists. The Chicago Tribune has filed numerous FOIA requests to access emails between the two men. No wonder they communicate mainly by phone.

Then there’s Sacks’s involvement with the stopgap state budget that brought the mayor a PR win in June—not because it solved malignant problems but simply because Chicago public schools will open in September. Axelrod credits Sacks with “shuttle diplomacy” in talks between Chicago and Springfield with John Cullerton, Mike Madigan, and Bruce Rauner. “He played a major diplomatic role,” Axelrod says. “He has cache with Rauner and could be blunt.” (Sacks and his wife, Cari, are friends of the Rauners, and Cari serves on the board of Diana Rauner’s Ounce of Prevention Fund.)

That doesn’t mean he and the gov agree politically, says Sacks, who supported Democrat Pat Quinn (unofficially, at least) in the last election. Sacks faults Rauner for his “attempt to bankrupt CPS,” which he sees as “foolish and dangerous and morally reprehensible. The CPS population is proxy for the neediest population, and you don’t use vulnerable people for leverage, and you don’t experiment on vulnerable kids.”

That bluntness applies to his relationship with Emanuel, too. “He has no inhibition about bringing Rahm bad news,” says Axelrod. “He’s utterly candid, brutally so sometimes, and Rahm tolerates it.”

Their friendship goes back to a meeting 15 years ago after Emanuel left Bill Clinton’s White House and reinvented himself as an investment banker. Sacks won’t say if he’s ever been on the receiving end of a Rahm tirade, pushing his own view of the mayor: “He’s sweet and caring inside. A great father—better than me—cares about people, courageous, smart, unbelievable work ethic.” And no, Sacks says, he never did a business deal with Rahm.

Is Sacks downplaying his role? My BS alarm buzzed after he said more than once, “I won’t hold it against you should you decide that I’m just too boring to write about.”

He urged me to please dump the political talk and write about his and Cari’s philanthropy. The couple quietly gave $1 million, for example, to the School of the Art Institute of Chicago; another million went to the Obama Foundation. (Sacks serves on its board.) He recently underwrote the Greater Chatham Initiative, an effort to bring jobs, businesses, and housing to several South Side neighborhoods, which should, as a bonus, help Emanuel regain African American support. Congressman Bobby Rush—an Emanuel-opponent-turned-backer and a recipient of Sacks’s campaign contributions—publicly and fulsomely praised Sacks for funding the program. And there’s Sacks’s favorite cause, Rahm Emanuel himself, to whom he has given more than $2.8 million over two campaigns, making him the mayor’s No. 1 donor.

Sacks does relish talking about GCM Grosvenor—not a hedge fund operator, although the firm does advise on them, but an “investment management business,” he specifies—which has $47 billion of assets under management and 485 employees (up from $225 million in managed assets and six employees when he arrived in 1990). “On financial issues,” Axelrod says, Sacks is a “genius-level asset.”

As for what this all adds up to: The Sun-Times’ Michael Sneed has reported that Sacks is “noodling” with running for governor. Some speculate Emanuel will quit the post after his second term—and Sacks will take his place. Sacks affects cluelessness about whether his friend will run again, saying, “I sure hope he will” and that the city would be lucky if he did. He also denies he’d run in Emanuel’s place: “The only thing I’m running for is the hills.”

Axelrod’s not so sure, given Sacks’s “passion for public policy. It wouldn’t shock me if he decided to go that route.”

Gubernatorial Buzz

Sacks isn’t the only local rumored to be eyeing the governor’s mansion.

Dick Durbin

The senator halfheartedly dismissed the gossip on Chicago Tonight, urging people who are speculating to “cool it.”

Chris Kennedy

The former Merchandise Mart head has toyed with the idea before, but reports say he’s more serious this time.

Pat Quinn

Because once (supposedly) just wasn’t enough—though the ex-gov has neither confirmed nor denied his interest.