Born on Zaebus Minoris, he was offered to the Chapter on the first full moon of his life. The tribesmen believe that the gods look down from the moon in judgement upon their children, so naturally, they invented a trial where they leave their babies alone for an entire night. During the night, those that are judged inadequate die, whereas the purest are taken by the gods to serve with them among the stars.
Loth was said to be a bloodthirsty warrior in his youth, and that lust for battle never faded away completely as he grew older. Unusually for a Librarian, he prefers to spar with other marines of his Chapter rather than spend his time meditating over arcane secrets or whatever it is that Librarians do. Much to the concern of his battle-brothers, he also likes to take the fight to the ennemy personally, seeking to slay enemy sorcerers and witches with the Magister's Axe. While the Red Scorpions commanders know they can't keep the irascible old warrior away from the front lines, the chapter tries it's best to keep him alive by assigning him an Honour Guard since they know his loss would be a bitter blow.
On the Tabletop
Cheesier than a fondue convention in Wisconsin for two editions, he's finally been toned down to a 'good-but-not-too-good' level. He can cast two powers and deny three; now that you always choose powers and with the removal of some of the more potent powers, he's lost a lot here. His most powerful trick of gaining a 2++ is completely gone, now he just gets a 2+/4++. He also has nothing to do with command squads now. The only things that stayed the same are his price and his anti-psyker skills; a 6" aura of re-rolls to wound vs Psykers and a +1S Force Axe that always inflicts 3 damage vs Psykers. Still good enough to be a nigh auto-include for any Red Scorpions player.