Wahshi ibn Harb is the person who killed Hamzah ibn Abdul-Muttalib (RA) at the Battle of Uhud in 3 AH, and who later accepted Islam. Wahshi was an Abyssinian slave renowned for his skill with the javelin. He was tasked by Hind bint Utbah (wife of Abu Sufyan) and his master Jubayr ibn Mut'im to kill Hamzah in exchange for his freedom, as Hamzah had killed Hind's father and uncle at the Battle of Badr.
During the Battle of Uhud, Wahshi found an opportunity and struck Hamzah with his javelin, killing him. After the conquest of Makkah in 8 AH, Wahshi eventually accepted Islam. The Prophet forgave him but reportedly asked him not to show his face, as it reminded him of his beloved uncle's death. Wahshi later participated in the Riddah Wars and is credited with killing the false prophet Musaylimah at the Battle of Yamama.
While Hind bint Utbah was the instigator and also later accepted Islam, she is not the one who physically killed Hamzah. Abu Sufyan was the overall Quraysh commander and also later became Muslim, but he did not kill Hamzah. Suhayl ibn Amr was another prominent Quraysh figure unrelated to this event.