Leo Caesius is one of AH.com's more intellectual members; he is known for his immense knowledge of linguistics as well as being fluent or semi-fluent in a vast array of languages, including Neo-Mandaean.

The Series version of Leo Caesius has him being the main computer for the AH.com ship and occasionally plotting the destruction of the crew when they annoy him. Although a robotic body was created for him, Leo tends to remain on the ship, due to the fact that once he downloads into the robotic body the ship cannot function.

Leo took on the Hermione Granger role in Luaky Commer and was 'C-Leo', the equivalent of C-3PO, in AH.com Wars.