Roger Clemens
Credit: Christian Petersen / Getty Images

Why he hung it up: Which time? Clemens "retired" in 2003, 2004, 2005, and 2007.

Why he returned: A combination of competitive juices and money. In 2005, he won the Cy Young Award. In 2007, he made about $1 million per start.

His success: Most of his comebacks were seriously successful, although his attempted 2012 comeback at 50 years old in the Independent League ended in failure.