Donald Trump’s personal attorney is under criminal investigation for his business dealings, has had his offices raided by the FBI, arranged a $1.6 million settlement between a GOP donor and Playboy playmate who became pregnant after an affair, and personally handled a $130,000 payout to porn star Stormy Daniels.

But in the months to come, it’s not Cohen, but another attorney—Jason Greenblatt—whose name might become a key component of Robert Mueller’s ongoing investigation of the president.

Greenblatt, reports Bloomberg, is the attorney whose knowledge of Trump’s business dealings is unparalleled. He began working for the Trump Organization in 1997, soon rising to the rank of in-house counsel and executive vice president.

Deals that passed through the company did so via his desk, rather than Cohen’s. (Chief financial officer Allen Weisselberg, was similarly involved in the company’s finances, says Bloomberg.)

Greenblatt was an employee of The Trump Organization for nearly 20 years. In late 2016, Trump named has as a special representative for international negotiations and assistant to the president. He most recently has served as a special envoy to the Middle East peace process.

Like Trump, he’s a fan of using Twitter to express himself. After Palestinian official Saeb Erekat circulated a letter to foreign diplomats accusing him of being a mouthpiece for Israel, Greenblatt replied via social media, calling it “self-indulgent rhetoric.”

https://twitter.com/jdgreenblatt45/status/984927997890351104

https://twitter.com/jdgreenblatt45/status/984928041204895745

Mueller, to date, has made no public mention of wanting to talk with Greenblatt. That’s not unusual, though, as the special counsel typically does not discuss his plans in advance with the media.