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.
An American Tail
Tiger makes his appearance when playing Poker with the other cats. He kept thinking they were playing Rummy, and blamed it on Warren T.'s violin playing. When Fievel is discovered, and tries to escape, Tiger is ordered along with the other cats to capture him. Tiger threatened to kill him while struggling to do so.
Eventually, after Fievel is caught, and put in a cage, Tiger is sent to be his guard. But he found Fievel crying, and asked him why he was crying. Fievel told him that he had to escape so he could find his family. Tiger is saddened at this, since he lost his own family. Fievel encourages him, saying he will find them. Then Tiger and Fievel begin to bond and share their interests, even singing a musical number about it. Then the alarm goes off, and Tiger allows Fievel to escape. Tiger is then fired by Warren, which Tiger finds a good thing as he tells his ex-boss off screen that he never liked him and that his music stinks.
He is next seen (somewhat briefly) when the Mousekewitz family teams up with Tony Toponi, Bridget and Gussie Mausheimer when they join together to find Fievel. Presumably, he teams up with them as well (albiet, off-screen). He serves as transportation for the other searchers. When Fievel is found, Tiger claims he's never been more happy in his life as Gussie hugs him on his big toe.
Tiger is last seen in the movie being carried by four of Henri's pigeons when flying to see the Statue of Liberty.
An American Tail: Fievel Goes West
Tiger plays a major role in this movie, and has a girlfriend.
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.