- – Ka'bandha, mere hours before Sanguinius makes Ka'bandha his bitch
"I-it's not like I care whether you live or die, lowly worms!"
- – Ka'bandha, during Devastation of Baal
Ka'Bandha, also known as Ka'Badguy and Ka'BanjoKazooie is a bloodthirster of Khorne. Several sources of fluff call him the most powerful servant of Khorne ever to manifest in the mortal realm. However, one of those sources of fluff was Matt Ward's 5th edition Grey Knights codex, so it conflicts with some other sources of fluff. Said other sources cite An'ggrath or Angron as the strongest servants of Khorne. While not explicitly stated, it is also heavily implied Doombreed is the strongest. Who to believe is up to you.
Ka'bandha during the Horus Heresy
Battle for Signus Prime
Ka'bandha is (in)famous for picking on the Blood Angels. After being summoned to the mortal realm along with a Keeper of Secrets by sacrificing a Word Bearer Astropath on Signus Prime, a major battle got underway. He promptly got into a mid-air fight with Sanguinius. After breaking Sanguinius's legs, he moved on to the Blood Angels, killing five hundred legionaries at once and activating the device known as the Ragefire at the height of the battle. This caused the dormant red thirst in the legion to awaken, messing up the Blood Angels' lives for at least the next ten thousand years.
Once Sanguinius had recovered from the minor inconvenience of putting his legs back together, he went back and challenged Ka'bandha to round 2, in which he managed to send him back to the warp.
Ka'banha returned during the Battle for Terra. He attacked Sanguinius when his back was turned (which Khorne probably didn't approve of), starting angel vs daemon: round 3. This time things were going fine until Sanguinius decided enough was enough, so he beat the shit out of Ka'banha and broke his back across his knee. He then threw the bloodthirster into the advancing army of heretics and took his well-earned rest by retreating behind the walls of the eternity gate.
The Grey Knights and Blood Angels team up to attack the daemon world Ka'bandha was on, in order to prevent his imminent predicted return to the mortal realm. Much fighting later, Ka'bandha is defeated using the sharpened femur of Brother-Captain Solor, a dead Grey Knight who killed Ka'banha once, a long time ago, and so his bones have some kind of special power against the daemon. Kalagazaar is subjected to Exterminatus. The surviving Blood Angels all have their memories wiped after the battle because that's what Grey Knights do.
999.M41, Baal system
Ka'bandha returns once more, along with a massive army of Daemons of Khorne, intent on wiping out those pesky kids once and for all. While the war between these Daemons and the Blood Angels is still quite an important ongoing conflict, Ka'bandha himself was defeated in single combat by the Sanguinor, by being choke-slammed from space and exploding in a crater of gore on impact. He does have a habit of getting the shit beaten out of him by winged entities in golden armour.
M42, Baal system
Set during the Devastation of Baal and the Indomitus Crusade, the Blood Angels and their successor chapters were defending against Hive Fleet Leviathan. The Blood Angels defense would not hold for long and as the final defense was broken something strange occurred. A Warp anomaly occurred and swept away the hive fleet. Every Imperial and Tyranid on the moon Baal Prime was dead and the skulls of the dead xenos were arranged so that they would create the symbol of Ka'Bandha on the moon. It would seem that Khorne had intervened and saved the remaining Blood Angels alongside the arrival of the Indomitus Crusade and Papa Smurf. It is also likely because he considers the Blood Angels and their descendants to be his prey and doesn't take kindly the idea of Space Bugs eating them all before he can annihilate them at full strength himself.
We can only imagine Ka'bandha looking away from the Blood Angels after this and claiming he didn't save them because he thought they were his worthiest rivals or anything, i-idiots (Bakas).
 Because, well... Internet.