Ganon is the main antagonist in The Legend of Zelda video games. (Thankfully he dropped his original name, Ganondorf.) A reader named Hillary mentioned the other day that she’d named her son Ganon after the character.
Ganon has never been among the most popular U.S. baby names. Gannon, on the other hand, has been in the top 1,000 since 2002. It ranked 889th in 2006. (Gannon is more likely to come from the surname than from the villain, though I guess you never know.)