The giant who attempted to rape Leto and was punished in Tartarus was Tityos.
Tityos was a giant in Greek mythology, born to Zeus and Elara in one tradition, although other accounts give him a different parentage. Hera reportedly encouraged or provoked his attack on Leto, who was the mother of Apollo and Artemis. Tityos pursued Leto, but her children killed him before he could carry out the assault.
After his death, Tityos was condemned to Tartarus, the deep underworld prison reserved for especially dangerous enemies of the gods. He was stretched out while vultures repeatedly ate his liver; because the organ regrew, the torture never ended. This punishment resembles the better-known torment of Prometheus, though Prometheus was a Titan and Tityos was a giant.
A common mix-up is with Porphyrion, another giant who fought the Olympian gods during the Gigantomachy. Polybotes and Alcyoneus were also giant adversaries, but neither is the giant identified with Leto’s attempted assault and the recurring-liver punishment.