Zeno Kuonji

Zeno is shown to be a kind-hearted, loving older brother to Stella.

After being murdered by Sid, and then resurrected by his mother, his personality changed, and he became a cold-blooded murderer and seemed to not remember Stella anymore. With time, his memories came back, and he went back to be Stella's loving older brother, but he was still chosen to be the Executor to the Kuonji family, therefore continued to be a murderer.
(Source: Wikia)