Marissa Mayer will be Yahoo Inc.'s fifth CEO in five years, not including two interim CEOs. She's also the fourth interim or permanent CEO this year. Here's a look at the people who have had that top job over the years:

Tim Koogle — 1995-May 2001. Began tenure shortly after Yahoo was incorporated in March 1995. Announced in March 2001 that he would step down after a replacement is found.

Terry Semel — May 2001-June 2007. Hired from Warner Bros. Stepped down under shareholder pressure.

Jerry Yang — June 2007-January 2009. Company co-founder and de facto CEO until Koogle started. Agrees to resign under pressure in November 2008, pending appointment of replacement.

Carol Bartz — January 2009-September 2011. Hired from Autodesk Inc., a design and engineering software company. Fired after failing to revive the company.

Tim Morse — September 2011-January 2012. Interim CEO. Retained chief financial officer role during CEO stint.

Scott Thompson — January 2012-May 2012. Hired from eBay Inc.'s PayPal. Left after disclosure that his official biography included a college degree he never received.

Ross Levinsohn — May 2012-July 2012. Interim CEO. Joined Yahoo in November 2010 following a stint running Internet services at News Corp.

Marissa Mayer — Starts as CEO on Tuesday. Most recently in charge of mapping, location and local services at Google.