Chirag Gupta is a minor character who moved away in the first Diary of a Wimpy Kid book. He is weird, He has a funny accent, and in Rodrick Rules, Greg and a couple other students play a joke on Chirag Gupta called the Invisible Chirag Joke, in which Chirag's classmates pretended that he was still gone after he had moved back. The joke lasted for a few days, until Chirag told his dad. In The Last Straw Greg plays another joke on April Fool's Day in which Greg and his friends spoke very quietly around Chirag to make him think that he was losing his hearing, but Chirag figured out what was going on pretty quick, and he went straight to the teacher to stop it before it became too big.
He's presumably the shortest person in his class (according to Greg he's in the 5% of kids wimpier than Greg). Telling by his name and hairstyle, he is presumably of Indian descent. Greg says that Chirag is small but he has a very powerful punch, and also that if school was based on height, kids like Chirag would still be in first grade.
He plays a pretty big role at the end of the first book. In Rodrick Rules and The Last Straw he plays more minor roles. Chirag does not appear in book four.