As the mightiest warrior to ever emerge from the Minotaur tribes of the Great Barrier, Alistar defended his tribe from Valoran's many dangers; that is, until the coming of the Noxian army. Alistar was lured from his village by the machinations of Keiran Darkwill, General Boram Darkwill's youngest son and commander of the Noxian expeditionary force. When Alistar returned, he found his village burning and his family slain. Bellowing with rage, he charged an entire regiment of Noxus' elite, slaughtering them by the hundreds. Only the intervention of some of Noxus' most skilled summoners checked Alistar's rage. Brought in chains to Noxus, Alistar spent the intervening years as a gladiator in the Fleshing, pitted in endless battle for the entertainment of Noxus' wealthy leaders.
Alistar's once noble soul slowly became twisted, and he would have been driven to insanity if not for Ayelia, a young servant girl who befriended him and eventually arranged for his escape. Suddenly free, Alistar joined the newly formed League of Legends to fight as a champion, hoping to one day exact his final vengeance upon Noxus and find the girl who had renewed his hope. Initially unwilling to cater to his celebrity status as a champion, Alistar has since discovered that there is power in fame, and he has become a vocal advocate for those whom the Noxian government treads upon. He also calls to light things that the Noxian military would prefer remain hidden -- something that has made him very unpopular with Noxus' nobles. His charitable work has earned him several philanthropic awards, which serve as an interesting contrast to the rage and destruction he brings to the League of Legends.
If you intend to grab the bull by the horns as a summoner, Alistar might have something to say about that.
Source: The Game Website.