The name of this peculiar cereal (and its mascot, both introduced in the Powerpuff Girls episode "Jewel of the Aisle"), is actually derived from four different cereal mascots:

Lucky the Leprechaun- Lucky Charms
Cap'n Crunch- Cap'n Crunch, of course
The Trix Rabbit- Trix
King Vitaman- From the obscure King Vitaman cereal