Powermasters, Seacons, Pretenders and Flywheels aren't obscure, since they exist in more than one medium.
Trannis was the young Decepticon warlord who took over after Megatron left Cybertron to chase the Ark. The Autobot Council, which had previously subjugated command to a now MIA Optimus Prime, resumed control -- effectively allowing for Trannis to conquer Iacon where he had the members of the Council executed, except for Councillor Xaaron who fled before the fall of Iacon. With the Council dissolved, Xaaron assumed a new title of Emirate, and founded the underground Autobot resistance including their special ops unit, the Wreckers. The Wreckers assassinated Trannis, who was then succeeded by Straxus.
I would've nominated Straxus, but he's technically no longer obscure since Hasbro made a Generations toy of him (Darkmount); and surprising even TakaraTOMY released their version (United Straxus) despite this character not appearing at all in Japanese continuity!
I'd also like to nominate Fang... he could come with a small PVC figurine of the Piano Transformer (Pianor?) that he beats the tar out of at Maccadam's.
