Soundwave is the spy master of the Decepticons. One of Megatron's earliest followers, and, many believe, instrumental to his rise, he uses his tentacles and a veritable army of Minicon Deployers to learn everything there is to know about his allies and his enemies. He was never very chatty, but these days, on Earth, he's become near silent, communicating by playing back recordings of other people's conversations. He just sneaks about, patiently looking for Autobot transmissions and creeping you out. Since the incapacitation of Megatron, Soundwave acts as a restraint on Starscream, reining in his rather volatile emotions, and ensuring that Starscream's less than subtle ambitions are held in check.
Soundwave has the ability to receive transmissions from anywhere on the planet, bar the shielded Autobot Base. This allows him to spy on every being on the planet in the hopes of picking up Autobot-related communications. He always keep Young Autobot alive.
He wasn't always a bad guy. He used Penny's voice to tell Gumball how Penny felt. He did the same with Penny, but this time using Gumball's voice.