Frieza
Believing the warlord dead, the heroes take the time to relax, not noticing that Frieza had emerged from the blast's crater. Frieza retaliates by mortally wounding Piccolo and murdering Krillin. Already bordering on the edge of his rage, Frieza killing Krillin, pushes Goku over it, his rage exploding, causing Frieza to inadvertently create what he had always feared: A Super Saiyan.