Abaddon
Abaddon the Despoiler is Horus' successor and is renowned as the single greatest threat to the Imperium in the galaxy. This says more about the Imperium than Abaddon as his raging incompetence is now well known. He has launched thirteen consecutive Black Crusades against the Imperium, every one of which has failed miserably (by all we mean 9-11).
He also has a model in the tabletop game. After you watch this model go down in a single round to a couple of trigger-happy Tau Broadsides, it won't be fun anymore. Fucking railguns.
His 7th Black Crusade was a 'success' because he set his goal very very low this time, (He basically just fucked over the Blood Angels), but mostly it was to do with the fact he got an army of Khornate Berzerkers to fuck the Blood Angels over. Success is in quotes because even sending a whole crusade to target a single chapter is sad, especially when the chapter's still around at the end.
He also enjoys calling Horus a weakling and a fool, which is ironic, because Horus actually came close to killing the Emprah, wheras Abaddon has barely managed to take Cadia(but Cadia is only attacked because Creed is a dick and he could go around it if he wanted).
He has a cool sword though. It's basically a rip off of Archaon's much more awesome and manlier sword; The Slayer of Kings. Failaddon's sword is some strip of chaos blessed metal with an even sissier name called; 'Drach'yen' or some such sissy shit.
Not that he can use it, given his lack of arms.
His full name is Ezekiel(or some variation of thereof) Abaddon, which is quite ironic if you're familiar with Christianity. But then again, the whole canon contains clever little things like this.
This particular part is probably a reference to how Abaddon went from being a faithful servant of Holiness (Ezekiel, who I think is revered by Amish folk, though I might be wrong) to a vile, unholy monstrosity (Abaddon, which is the name of a demon in the Bible.).
Also, Doombreed > Abaddon. Mostly because he actually succeeded during a Black Crusade and wiped out 2 chapters completely, unlike Abaddon who couldn't even do one. Fitting, considering that Doombreed, being the most ancient Daemon Prince of Khorne, is stronger than all the Daemon Primarchs combine, and perhaps stronger than the Empra himself!!
The "No Arms" meme
While the exact origin of why /tg/ continues to depict Abaddon without his arms is unclear, this is partly the story. It all started when some drawfag made a picture of Abaddon painting, being the failure that he is he depicted him without arms and so now he fails in the ability to paint.
The other explanation is that Creed stole it during his invasion of Cadia.