Nothing is safe. From raw ore to living robots, it all goes into Mixmaster's grisly drum where it's reduced, refined, and recombined into virtually any raw material the Decepticons need. Watching Mixmaster prepare a new batch of materials is like seeing some mad alchemist at work, giggling and cackling over his creations with evil glee. It would be a stretch to call him a scientist; a better comparison would be to a witch throwing arcane scraps into her cauldron to complete a bubbling potion. His fellow Decepticons suspect Mixmaster of having a few wires loose in his logic center, but they can't argue with the results. He transforms into Devastator's left leg.
Mixmaster's origins are muddy. He was supposedly alive on Cybertron several million years ago, where he helped create Megatron. Five Faces of Darkness, Part 4 According to Omega Supreme, however, Mixmaster and the other Constructicons were nice guys back then and built Crystal City which Omega guarded. This changed when Megatron attacked the Constructicons with his Robo-Smasher, effectively reprogramming them into Decepticons. The Secret of Omega Supreme
In 1984, Mixmaster and the Constructicons were stationed on Earth, where Megatron claimed to have built them. One of their first missions was to sabotage the Autobot computer Teletraan I while the Autobots were distracted, and Mixmaster helped by mixing up an acid strong enough to melt through solid rock and the floor of Autobot headquarters. Ultimately they were driven back by the Dinobots and despite forming the mighty Devastator, they were knocked into a river of lava. Heavy Metal War The Constructicons survived and continued to work with Megatron during his various schemes. During one such scheme, namely the reconstruction of New York City into New Cybertron, Mixmaster repeated himself a lot ("Auto-auto-autobots!"). This 'never' happened again, but everyone assumes it was his standard vocal quirk anyway.