This is - probably - the last Transformer who will show up on this list as we enter the home stretch. And he's here for one simple reason: Soundwave was cool. Like, Rat Pack meets Star Wars cool. You're talking about a giant robot who turns into a tape deck and plays den mother to a bunch of smaller robots who can turn into cassettes. There was nothing more awesome than that in 1983.
Beyond how cool of a concept (and a toy) he was, Soundwave as a character was fantastic. With his modulated synthetic monotone, his smug, aloof arrogance, and his belief in his own superiority, Soundwave was like the fraternity brother who popped his collar before anyone else, who stood in the back and spiked the punch to laugh to himself while everyone else got sick, and who always gravitated to the strongest bully in the crowd to enable his cruelty. He's a blackmailer, an opportunist, and his own teammates can't stand him but have to put up with him because he's so good at what he does. He's that awful combination of star player and conceited jerk we all know so well.
Plus, if you messed with him, he could pop out like a dozen diminutive gang members like Rumble and Frenzy and Laserbeak to mess you up.