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. He has a particular interest in the Middle East.

A popular pasttime is 'finding Leo's umlaut', referring to his real life name. He rarely replies to posts referring to this.

He's usually considered fairly left-wing, or perhaps it's more accurate to say that he just distrusts the current Republican leadership in the US. His most common right-wing political foil in discussions is Paul Spring.

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.