A brief explanation why…
Michael Dell: After serving as CEO for two decades, Dell left the position for then-president Kevin Rollins. Dell remained as chairman of the company's board and in January 2007 he resumed his role as CEO at the request of the company board.
Steve Huffman: Created Reddit with classmate Alexis Ohanian in 2005 and sold the site to Condé Naste a year later to pursue other projects. Huffman later admitted regret over selling the service and he returned as CEO in 2015 after controversy surrounding interim chief Ellen Pao.
Steve Jobs: Forced out of Apple after losing a power struggle with CEO John Sculley (1983-1993), Jobs later recounted that it freed him to enter one of the most creative periods of his life, which included co-founding the Graphics Group, which later became Pixar Studios. Jobs returned to Apple as CEO 1997.
Larry Page: Serving as Google's CEO from 1998 through 2001, Page stepped aside in August of that year to let Eric Schmidt guide the company through its initial growing pains and IPO, not least by lending more credibility to investors than the twenty-something co-founders Page and Sergey Brin could. In 2011, Page reassumed his role as the CEO of Google (now the CEO of its parent company, Alphabet Inc.).
Jeff Bezos: Founding Amazon as an online bookstore in May 1996, Bezos has always been the company's CEO.