Tiger is the deuteragonist in An American Tail and its sequels, despite originally being a villainous cat, Tiger would quickly become Fievel Mousekewitz's best friend and ally: not only aiding the young mouse in escaping the clutches of the evil Warren T Rat's gang but also providing valuable help to Fievel throughout his later adventures in the Old West and beyond.
He was voiced by the late Dom DeLuise.
An American Tail
An American Tail: Fievel Goes West
An American Tail: The Treasure Of Manhattan Island
An American Tail: The Mystery Of The Night Monster
Despite his formidable size Tiger is a harmless feline who despises violence and is actually very affectionate towards all living beings, even mice - he doesn't share the almost universal hatred of mice that many felines in the series did and indeed was willing to fight in defence of the downtrodden (though he was not much of a fighter, though he had his moments).
Tiger was once a member of Warren T Rat's gang but was clearly unhappy with his position, when he first met Fievel he attempted to act like a tough and mean cat but was unable to hold the act together long and he befriended Fievel: the two have remained close ever since.
Fievel and Tiger's friendship is an innocent one and is sadly very rare, which can cause mild problems as most mice are not used to having an affectionate feline in their midst: even Fievel's father noted that when Fievel grew older he may have to rethink having a cat as a friend - however given Tiger's nonthreatening nature these words of warning may not be true and he is in many ways a pioneer for mouse/cat co-existence.