Nobody is taking over for Graves as Uber's senior vice president of global operations, and there are no plans to fill the role immediately given all the other vacant executive positions, a source familiar with the matter told CNBC.

Ryan Graves — one of the company's first employees, the first full-time CEO, and one of its biggest shareholders — said he will transition out of his operating role and remain on the board.

One of Uber's original employees — and one of former CEO Travis Kalanick's top boosters — is stepping down from his leadership role at Uber.

Ryan Graves was Uber's first full-time CEO and employee, who was last senior vice president of global operations before announcing he would step down in August 2017. Graves said at that time he would remain on the board during the search for the replacement of his CEO successor, Travis Kalanick.

As a board member, Graves will still be involved in finding the replacement for his successor, Kalanick. While Graves and Kalanick have long been close, recent reports from The Information indicated that Graves' ties with Kalanick might be unraveling.

Graves' involvement in Uber's recent scandals thrust him into the spotlight earlier this year.

In particular, Graves was aware of "greyballing," a tool Uber used to evade authorities around the world, according to The New York Times. That program is now subject to a criminal probe, Reuters reported. An Uber insider told Business Insider that Graves, known as Uber's "Mr. Nice Guy," had "vanished from the office," and that employees feel Graves hasn't displayed the leadership they would have expected. Recode reports that Uber's HR — accused by a former employee of dismissing sexism allegations — reported to Graves.

Graves, who was relatively inexperienced before his serendipitous start at Uber, has been key in launching Uber's expansion into international markets and defining the company's core values, like "super pumpedness." He's one of the executives that's said to be leading the company, which is currently without a CEO.

He has been overseeing UberEverything (which includes UberEats and UberRUSH). Jason Droeg, head of Uber Everything, will continue to head it with his current title.

Early Uber investor Chris Sacca tweeted on Thursday that he was grateful Graves took a huge risk on Uber. When Graves started at Uber, Kalanick had been running the tiny San Francisco company on a temporary basis, dropping by 15 to 20 hours a week.

"His grind was relentless. Legendary. Uber was launched in zero cities when he joined and operates in over 600 cities worldwide today," Sacca tweeted.

Tweet: Within the Uber boardroom, @ryangraves is the director most consistently respected by the others and is great at building consensus.

"There is another lesson I've learned that we should have applied much earlier," Graves wrote in an email obtained by CNBC on Thursday. "We should have taken more time to reflect on our mistakes and make changes together. There always seemed to be another goal, another target, another business or city to launch."

Here's the full email that Graves sent to colleagues: