Originally Posted by
Sky Shadow
Death's Head was a non-transforming, non-Transformer robot from the future who was blown up to Cybertronian size and became a bounty hunter. He was then sent to 2007ish by The Doctor. (From Doctor Who. No, really.) Death's Head then timetravelled back to 1987 to hunt for Galvatron but was prematurely sent back to 2007 by Wreck-Gar. He then hunted Rodimus Prime, but Prime paid Death's Head more to hunt Cyclonus and Scourge instead. Death's head then defeated Unicron (with a bit of help) and travelled through time again. He met The Doctor again, who shrank him back down to human size using The Master's Tissue Compression Eliminator and sent him to 8162. Where he did lots of stuff with lots of people, none of it directly related to Transformers.
Death's Head II was originally Minion, a cyborg from 2020 who was an amalgamation of personalities owing to him sucking the skills out of a variety of people, but when he tried to do it to Death's Head, DH's personality became the dominant one. (Supposedly, although he stopped liking money and bounty hunting and became a hero instead. He didn't have anything to do with Transformers. Well... only very indirectly... like... he did some uncanonical stuff with Spider-Man just like Gears and Megatron did some uncanonical stuff with Spider-Man.)
Death's Head III is a cyborg from the 22nd century who allegedly precedes Death's Head (I). He didn't hang around with Transformers.
And there's even more time travel involved than just the bits I mentioned.
(Oh - and S.W.O.R.D. is an awesome comic - Kieron Gillen is a legend.)