∟ Ron & Judy Witwicky William Lennox Listen up! You wanna hit back? We’re gonna have to wingsuit in. It’s the only way to get close. I can’t promise anyone a ride home, but if you’re with me, the world needs you now.
They’ve had human allies, but such alliances tend to be temporary and last only the length of the episode in question! Further, such alliances tend to be the result of the Decepticons captured, forcibly coercing, or otherwise tricking humans into working with them, so I doubt that’s the story of thing you’re looking for, nor are you really thinking of “equal partnerships” like Starscream working with MECH in Prime, or Blackarachnia working with Meltdown in Animated.
Still, the most famous human-who-worked-with-the-Decepticons is probably Doctor Arkeville from the Generation 1 cartoon, who provided the Decepticons with mind-controlling hypno-chip technology, and believed the Earth would be his to rule once Megatron was done with it:
He’s reocurred several times in Japanese continuity, and built a few of the versions of Nemesis Prime that are out there.
Shawn Berger was tricked by the Decepticons into thinking that the Autobots were the true villains, who had manipulated the public’s image of the ‘cons – but he wasn’t a nice guy himself either, only agreeing to help them “straighten out” their image in return for political power.
There was also Abdul Fakkadi, ruler of the nation of Carbombya, who allowed the ‘cons to hide out in his country and drink his oil in return for… well, dude just really liked money and ostentatious gifts.
In the Marvel comic, Donny Finkelberg worked with the Decepticons for a while, providing them with a “cover story” that disguised their alien nature by pretending to be a supervillain named “Robot Master” so that the public would think the Transformers were his creations, rather than otherworldly visitors.
I feel like the closest there’s been to a true “Decepticon human companion,” in the same style as the traditional Autobot human companion role someone like Spike fills, is Dylan Gould from Dark of the Moon. He and Soundwave were played as a bit of an “evil Bumblebee and Sam.”
Also in the realm of live-action movies, the “Human Alliance” toyline featured some Decepticon human ally characters, Sergeant Chaos and Master Disaster, former NEST soldiers gone bad. The movie “Transformers Classified” novels also had Douglas Porter, a son-of-a-millionaire spoiled brat who worked with the Decepticon Reverb to get back at daddy.
Solon Kitakaze could count as a “human companion” for the Decepticons methinks. Deathsaurus’ adopted son!
“It’s even uglier from close up,” Sari commented as she leaned a little over the railway, only to be deftly caught by the collar of her dress and forced back by Captain Fanzone, who was frowning.
“What did I told you already about getting too close, kid?” he grumbled. “Those things are anything but safe, and you have no business nearby!”
“Hey, relax, Captain, I got my own bodyguards with me!” Sari gestured to the pair of Autobots who were also watching the creature in the aquarium at a short distance from them. Mouth agape, Bumblebee could only shake his head in disbelief.
“Primus on a pogo stick, I didn’t know Meltdown made them that big!”
“Indeed,” Prowl murmured with a raised optic ridge. “I do not believe this shark-like creature was that big when we first encountered it.”
“What did he do? Feed him growth hormones?”
“Or most likely, tweaked their DNA further,” the Cyber-ninja commented as Sari and the Captain joined them. “I trust you will be able to contain this… creature without further help from our part?”
“Sure, sure, no biggie,” the Captain waved asides, though he was clearly sarcastic. “You know, the guys at the department were feeling humorous. Did you know they decided to give it a name?”
“Indeed, Captain?” Prowl asked. “And what should that be?”
For all answer, the human gestured at one side of the aquarium, where someone had painted in bright red letters the words ‘Black’s Lagoon Creature: beware!’. Sari couldn’t help it; she guffawed.
Cybertronian Database 