Uber's long-time chief business officer, a close confidant of Travis Kalanick, is leaving

Uber's long-time head of business, Emil Michael, has left the company, according to an Uber spokesperson.

Michael emailed his team on Monday saying Sunday had been his final day at the company after nearly four years leading its business strategy.

"I signed on with the company almost four years ago and it has truly been the experience of a lifetime helping Uber become the fastest growing company of all-time -- spanning 75 countries with over 14,000 employees," Michael wrote in his goodbye letter first posted on The New York Times.

The Wall Street Journal reported on Sunday that Michael was expected to resign. In his letter, Michael said David Richter, Uber's current VP of Strategic Initiatives, will be taking over the position of SVP of Business.

Michael played a pivotal but oftentimes controversial role in building Uber into the $69 billion ride-hailing giant it is today.

As one of Uber CEO Travis Kalanick's closest confidants, Michael oversaw Uber's broader business strategy, including partnerships and fundraising. He had been with Uber since 2013 and his last title was chief business officer.

Michael's departure comes amid an investigation into Uber's work culture, including several scandals in which he was known to have a direct role.

In 2014, Michael threatened to dig up dirt on a journalist who covered the company. He was also one of the Uber executives who went to a karaoke bar in Seoul on a business trip that same year, where executives reportedly selected women to be their companions for the night by the numbers hanging around their necks. Michael also allegedly saw the medical reports of a rape victim that had been obtained by another Uber executive, Recode reported on Friday. That executive was subsequently fired after journalists started investigating the story.

The recommendations from the months-long investigation into Uber's workplace, being led by former attorney general Eric Holder, were unanimously approved by Uber's board members in an emergency meeting on Sunday morning in Los Angeles.

In his note Monday, Michael said he was not only proud of raising more money than any other tech company in history, but also building a diverse business team within Uber.

"As an Egyptian immigrant who was taken under the wing of a great business leader like Bill Campbell, I have an abiding belief that we all should pay it forward by ensuring that our workplace represents all types of people," Michael wrote. "Uber has a long way to go to achieve all that it can and I am looking forward to seeing what you accomplish in the years ahead."