Last week, it was announced that David Blake, one of the original founders of Degreed returned  to the position of CEO with the acquisition of his latest startup Learn In.  Degreed was the early leader in defining the learning experience platform (LXP) market. Over the last 5 years, many others have tried to emulate this as well, and the lines between a traditional learning management system (LMS) and LXP are getting murkier by the month. The LearnIn acquisition gives Degreed another competitive advantage of managing tuition and payments as well as the ability to build talent academies to help attract and retain skilled talent. 
Degreed was an early adopter of skill verification and upskilling as well as a labor marketplace with the addition of Adepto. When David left Degreed (as CEO but remained on the board) to his co-founder Chris McCarthy, the company was rapidly growing and had hired some of the best people in the industry. Later, Chris left to tour around the U.S. and homeschool his kids in an RV, a new CEO, Dan Levin, came in from outside the industry. During this time, innovation, marketing, and positioning seemed to stall and competitors such as CSOD (EdCast) and others gained significant traction. 
David has always been an innovator. The future for Degreed once again looks promising and I bet the big 3 (SAP, Oracle, and Workday) are circling.
What other high profile CEO left his large company under stressful terms and then returned to the industry to become a dominant player?