Senior vice president of advertising and commerce Sridhar Ramaswamy is leaving the company after 15 years to join the venture capital firm Greylock Partners. He’ll be replaced by Prabhakar Raghavan, a Vice President of Engineering at Google who has lately been overseeing Docs, Drive, Gmail, and other productivity apps.

Google’s ad business is now responsible for more than 85% of parent company Alphabet’s revenue, but it’s facing challenges as ads are becoming more costly to serve on some devices and platforms and as concerns about online privacy raise questions about how Google collects data and targets advertisements.

At Fortune‘s Most Powerful Women summit this week in Laguna Niguel, Calif., Google and Alphabet CFO Ruth Porat suggested the critiques of Google over data protection were unfair. She told Fortune‘s Pattie Sellers that privacy had been important to Google since it was founded, and that “‘respect the user’ is a key mantra internally.” She also implied that the burden of leading the way on privacy issues lies with the tech companies, saying “we need to constantly raise the bar on ourselves.” This stands in contrast to calls from some tech executives for national law regulating the sector.

Google (GOOGL) celebrated its 20th anniversary of incorporation last month.