Alvin, Simon and Theodore are anthropomorphic chipmunks in The Alvin Show and Alvin and the Chipmunks. They have been featured in cartoons, movies and crossovers alongside their adoptive father and manager Dave Seville.
The three perform as a musical troop plying their talents as a sort of high pitched a cappella troop. Their style is considered a success in-universe which has earned them fame, moderate wealth and celebrity status. Their cartoons and movies usually feature at least one song each and generally rely the chipmunks dealing with the pressures of fame or leaning personal life lessons. All three tend to create more than a large fuss for Dave as their manger/surrogate father.
Alvin is the self-proclaimed leader and also the middle of the Chipmunks, sporting a red shirt with a large "A" on it and a tone of conceit. Alvin is easy to tell apart from his brothers and often is the focus of the life-lessons being touched upon. Alvin is brash, proud and arrogant but never callous to his fans or brothers.
Theodore, the smallest and also youngest chipmunk due to his youthful appearance and the tritagonist of the first two films and a supporting character in the rest of the films, is clad in green and often can be distinguished from his two older brothers as the worrywart of the crew. Theodore tends to be shy and prudish compared to his brothers while also easily the kindest. Most of Theodore's problems stem from his less than assertive nature and any life-lessons touched upon for him mostly involve him overcoming his demure nature.
Simon is the tallest and the oldest chipmunk and the deuteragonist of the first two films and a supporting character in the rest of the films, and easy to pick out with his long blue shirt and glasses. Simon prides himself on being the most intelligent of the three and the most sophisticated, life lessons taught to Simon usually focus on teaching humility...or can be as simple as just never trusting Alvin over his own good sense.