CM Punk was the ring name of wrestler Philip Brooks, who became a WWE champion.
Brooks was born on October 26, 1978, in Chicago, Illinois. He adopted the name CM Punk during his independent-wrestling career and carried it into WWE. The initials have been given different explanations over time, but the company generally treated CM Punk as the established name rather than requiring one fixed expansion.
Punk won the ECW Championship in 2007 and later captured the World Heavyweight Championship and WWE Championship. His 2011 storyline, including the famous July 2011 speech known as the “Pipe Bomb,” made him one of WWE's most prominent performers.
The answer is sometimes confused with his legal name, Philip Brooks, or with his nickname “The Best in the World.” Those are not separate ring names. Punk also became known for his straight-edge lifestyle, which was incorporated into his wrestling character.