Ouroborus is one of the many TVA agents, who as we know have all been abducted from their own timeline by 'he who remains'. In his actual life before the TVA, he was a writer and a scientist, although he preferred the prior.
His technical skills were put to work at the TVA, where he now works in repairs and advancements. On top of this, he's also the co-author of the TVA guidebook.
O.B. as he is colloquially known has a very enthusiastic and helpful personality, helping Loki and others to fix the timeline troubles.