Mack, when "formalized" with the final k, makes an engagingly amiable choice, a far more uncommon option to the ubiquitous Max and Jack, with a nice, every-guy feel. Mack entered the popularity list in 2009 for the first time since 1989 and continues to climb. However, it's still far from its peak -- it was a Top 100 name in 1900.
Mack (born Michael) Sennett was the innovator of slapstick comedy in silent films. The name is also suggestive of Mack the Knife and a whole family of computers. Kevin Kline, Cuba Gooding, Jr., Dan Aykroyd, Eric Roberts and Snoop Dogg have all played characters named Mack.