Donal is another child that grew up in the same Cimmerian village as Conan.
The two were good friends but Conan, although smaller, was brighter and the other children followed him. This created a jealously in Donal. The jealously may not have been there initially but Donal's father was jealous of Conan's family. Donal's father would insult Conan's family at length to Donal which created this new resentment toward Conan.
One day, sick of Conan dealing out the roles in a childhood game, Donal attacks Conan. All the other children defend Conan and this builds on Donal's resentment toward him. Donal later attacks Conan when he is only with Tarra, the only girl in the group of children. Conan, uses a sword for the first time to defend himself after being severely beaten by Donal. He cripples Donal permanently.
As an adult he's known as Donal the Cripple, because of his disability he develops cunning and intellect and his voice carries weight in his clan.
During Aquilonian invasion on Cimmeria southern marches he's captured and crucified by Aquilonians. His death incites Cimmerians to attack on Venarium.