Sarpedon.
No, Zeus did not kill Apollo, nor did he attempt to. Besides, Apollo is immortal and cannot be killed. Apollo's son the god of doctors was killed by Zeus.
Perseus.
Perseus, son of Zeus
Patroklos was the friend and comrade of Achilles. Hector killed Patroklos believing him to be Achilles.
Zyzz Shaversarian
Castor, the son of Zeus and Leda, was mortal while his twin brother, Pollux, was immortal. Castor was killed in a battle, while Pollux, devastated by his brother's death, asked Zeus to let them share their immortality. As a result, Zeus placed them both in the sky as the constellation Gemini.
Hercules was the son of Zeus. He killed the snake-headed Hydra, but she was not usually called a Titan.
I'm going to assume that you're asking which son of Zeus killed Medusa, in which case the answer would be Perseus.
Hera has hurt and killed a lot of people because of the way Zeus cheated on her and she killed all the women she found out about him cheating.-----------------------------------------------------------------------------------------------Note: Hera was not a person she was a "mythological" goddess. Therefore "bad person" could not apply.
demigod son of zeus, killed medusa
No, he did not. The hero Perseus killed Medusa. Perseus was also Zeus' son but his mom was mortal.
Perseus, the son of Zeus and Danae.