Louis is an companion of Letho of Gulet who advised him to hide in Velen in Reardon Manor and later betrayed him because of Nilfgaardian bounty hunter Arnout Vester. Letho describes story between them two as following:
Was before Foltest kissed this world goodbye. Louis was a wanted man in Aedirn. Hefty bounty on his head, and normal contracts were hard to come by. So I decided to catch the bastard, make some coin. Tracking him down proved easier than killing a drowner. He was, uh, merrymaking at the Golden Hanged Man, smack in the middle of Hagge. Nabbed him, tied him up, but the guard post didn't open till dawn... so we had a few hours. Started talking, killing time. Chat was so nice that once dawn came I let him go.