Cratus - God of power and strength
Chiron - Trainer of heroes, a centaur. Was different from other centaurs because he had the front legs of a human, not a horse
Charybdis - A giant whirlpool monster
Centaur - A creature half horse half man, had the legs and body of a horse, but the chest and head of a human.
Circe - A witch who turned humans into animals
Clio - One of the nine Muses, represented history
Chimera - A two-headed creature with the body of a lion (one head was a lion's the other a goat's)
Charon - Hades's ferryman, pulled souls across the river Styx
Cerberus - The three-headed black guard dog of the Underworld
Cyclops - A one-eyed giant
Clothos - One of the Fates, cuts the thread of life
Tell me if I missed anyone/anything!