Hauler is a Constructicon, and one of the only Constructicons that was not reprogrammed into a Decepticon. This has led him to join the ranks of the Autobots.
His first and only officially recognized anime appearance thus far was in Transformers G1 episode 1, though it is entirely possible he was later a part of the Decepticons, as there were some nameless Constructicons who would make cameos, one resembling Hauler, and the background story of the Constructicons states that they were once Autobots before being captured and reprogrammed. But this is sheer speculation, and as things officially stand Hauler is not only the first Constructicon ever seen in animation, but his first appearance is also his last.
Additional notes: Hauler is not to be confused with Long Haul who is a very different Constructicon. Hauler's only official G1 appearance was re-released as the first episode of Transformers Generation 2, but this was the exact same episode with some CGI additions and minor audio changes He may or may not have also appeared in the episode The Master Builders, a Constructicon who heavily resembles him but is not acknowledged as Hauler appeared in this episode, and since it featured Autobot and Decepticon constructicons working together it is very possible it was him.