It's official. The former CEO of Expedia has begun his job as the new Uber CEO, and he knows it's not an easy job. In a memo to his now former employees, Dara Khosrowshahi, 48, says, "I have to tell you I'm scared." He wrote, "This has been one of the toughest decisions of my life. I've had the privilege to run Expedia for 12+ years now, and most of you who have been on this journey with me know it has not been easy going."

It may not have been easy at Expedia, but Khosrowshahi faces a challenge of a lifetime at Uber.

He will be off and running today, as he steps in to clean up the mess left behind. There are massive controversies around Uber, including sexual harassment and discrimination allegations, a high-profile lawsuit from Google's Waymo (formerly the Google self-driving car project), as well as a federal probe into the secret Greyball tool used by Uber to deceive and evade regulators who were trying to shut down its ride-hailing service.

As if that's not enough for a new CEO to manage, there are accusations of mishandling of a rape victim's medical files in India and, most recently, a federal probe over possible foreign bribery law violations.

After much deliberation, Khosrowshahi says he's prepared to face these issues head-on. While he may be scared, and justifiably so, he also thinks the challenge will be fun.

In an interview at Expedia's headquarters in Bellevue, Washington he said, "Are there difficulties? Are there complexities? Are there challenges? Absolutely, but that's also what makes it fun. I am not in this to coast. I'm in it to get my hands dirty and build a team and do something that people will look back on with tons of satisfaction."

In a memo to Uber's employees, Uber's board said, ""We're really fortunate to gain a leader with Dara's experience, talent, and vision. The board and the executive leadership team are confident that Dara is the best person to lead Uber into the future building world-class products, transforming cities, and adding value to the lives of drivers and riders around the world while continuously improving our culture and making Uber the best place to work."

Uber's board included the job of taking the company public in the new CEO's job description, and Khosrowshahi says he'll be ready for the green light. "At some point, I expect the company to be public, but that's up to the board."

Good luck Dara Khosrowshahi, you're a brave man.