Miles is the son of Samantha, and a main character, in the fourth CGI/live-action film Alvin and the Chipmunks: The Road Chip. Though he's initially portrayed as an antagonist, his role as such decreases drastically as the film progresses.
Alvin and the Chipmunks: The Road Chip
At first interaction with The Chipmunks, Miles is shown to be a bully due to his dislike for the group: he hangs Theodore on a windmill, hits Alvin with a golf club, and locks The Chipmunks out of their own house. After he learns of a potential proposal between his mother and Dave Seville, he agrees to work with the three brothers so none of them will have to deal with each other as a family.
During the trip to Miami, the boys bond and it's revealed that Miles' father left him when he was younger, tarnishing his appeal of fathers in general. At the party in New Orleans, Miles' attitude towards The Chipmunks changes to one of acceptance. As a result, he's greatly upset when the boys are celebrating after they believe they've successfully stopped the proposal. He learns that they still wish to hang with him regardless after Theodore risks his life to save Miles from being hit by a car.
When he sees Ashley, the artist Dave's producing for, after the final performance with The Chipmunks, he immediately develops a crush on her and is invited to a party in L.A.