Soundwave is the Decepticon communications officer, totally loyal to Megatron, with great battle prowess, and a minature army of Spy Cassettes to back him up!
On Cybertron, Soundwave acted as a spy, frequently posing as a structure on the outskirts of Iacon, where he could deploy his cassettes to observe Autobot plans. It was while on a mission such as this, that he learned of the Autobots plan to search out energy on new worlds. When the Decepticons boarded the Ark, Soundwave showed exceptional strength, taking on, and defeating, three Autobots at once.
After Teletran One reactivated the Transformers, Soundwave gained the ability to transform (shrinking as he did so) into a personal cassette player. In this mode, he and his tapes can record information through a built-in microphone - more inconspicuous than deploying a cassette to record it solo.
Soundwave can maintain radio contact with his cassettes, and is able to read the minds of other Transformers through detection of electronic impulses. It also seems that Soundwave is equipped with a chest-mounted device capable of producing the framework for Energon Cubes. This seems to have been later ignored, as Decepticons were seen pulling the frameworks out of subspace.
Sounwaves served the Decepticon cause without question, when in the Earth year 2005, when the Decepticons launched a massive assault on Autobot City, Megatron was critically injured by Optimus Prime. When Starscream threw Megatron into space during the return flight to Cybertron, and tried to claim leadership of the Decepticons for himself, Soundwave, acting out of character, or perhaps only revealing his true nature for the first time, ejected his cassettes, and tried to assume the role of leader himself. However, when Megatron returned as Galvatron, Soundwave snapped back to his old loyal self, following the orders of the unhinged Decepticon commander without question.
The final fate of Soundwave is not recorded. It is known that at least one of his cassettes (namely Ravage) was granted amnesty after the wars ended, but it is doubtful the same leniency was shown to Soundwave. This supposition has recently been reinforced, when what appeared to be the shattered remains of Soundwave were seen in a mass grave on Cybertron. It seems possible that the Megatron of the continuity known as 'Beast Machines' extracted Soundwave's spark and used his body in production of Vehicon drones.