Baine originally came into the Warcraft storyline after he was kidnapped by murderous centaurs. His father Cairne, Chieftain of the Tauren, enlisted the help of Thrall, Warchief of the Orcs, to rescue him, leading to the two races becoming strong allies.
Baine first appeared in World of Warcraft
as a low-level quest giver, the leader of a small community of Tauren in Mulgore called Bloodhoof Village, an area for low-level Tauren players. However, with the death of Cairne in the events leading up to the Cataclysm
expansion (Cairne was killed in an honour duel with Garrosh Hellscream
, who had taken the throne of Warchief from Thrall), Baine has stepped up to become Chieftain of the Tauren. And for obvious reasons, Baine and Garrosh are nowhere near as close as Cairne and Thrall were, so relations between the Orcs and the Tauren are not as strong as they used to be.