What was the childhood name of the hero Cú Chulainn?

The childhood name of the hero Cú Chulainn was Sétanta, also commonly written Setanta.

He was born into the Ulster Cycle and was raised as a gifted boy on the Muirthemne Plain. In the Táin Bó Cúailnge, stories of his childhood describe his remarkable athletic ability and his early encounter with the boys’ troop at Emain Macha. His transformation into a formidable warrior is linked to both his skill and his supernatural battle frenzy, or ríastrad.

Sétanta became Cú Chulainn after killing Culann’s fierce guard dog in self-defence. Rather than leave Culann unprotected, the boy offered to serve as the hound’s replacement until another guard could be raised. The name therefore means roughly “Culann’s hound,” though cú could also carry the figurative sense of warrior.

Conall, Lugh and Finn are separate figures. Conall Cernach is an Ulster hero, Lugh is Cú Chulainn’s divine father in many accounts, and Finn belongs to the Fenian Cycle rather than the Ulster Cycle.