Asmodai

"'DID SOMEONE JUST SAY 'MURDER ANYONE VIOLENTLY'?!'"Asmodai is the Master of Repentance of the Dark Angels.

Official Canon
Asmodai is the most obsessed with capturing the Fallen among his brethren, taking great pains to find them and great pleasure in getting them to repent. He is also extremely strict with his duties as chaplain, discouraging laughter and punishing tardiness, threatening officers when he doesn't get his way, even costing them victories and angering allies to chase rumors of Fallen. He has also only succeeded in making two Fallen repent.

Nonetheless, Azrael keeps Asmodai around because there's no one more relentless at tracking down Fallen.

TTS Canon
Asmodai is even more unstable, as he will automatically interpret "repent" as "murder as violently as possible." He is extremely rabid and is foaming with rage (or murderous excitement) at all times.

He also seems to have a silly side, in pestering Azrael, by repeatedly asking if 'they were there yet,' on their travels to Orior, even as they were right above it. Azrael responded with growing irritation at him and his 'references' (presumably to either Nappa from Dragon Ball Z Abridged, or to the Simpsons, though how he'd know is unknown).