Riddler is an adult who is a stickler for the rules, but that doesn't mean he's not fun-loving. He enjoys playing childish pranks (even at inappropriate times) and tries to enjoy life as much as he can. That is, when he's not asleep. He will fall asleep in strange places and is almost always sleepy. He's a little oblivious to insults or compliments, which might make him look dumb. Underwood blindly follows authority and the law and as an Alpha, will impose the rules on law-breakers. The fact that he's missing his right arm doesn't seem to bother him in the least.
(Potential Spoilers ahead if not up-to-date with comic)
Riddler had been working for the Alpha after his Tertiary training that came after Acceptance. He was working (and sleeping) on the job as usual one day, and after being scolded by his superior, returned to a case that was handed to him. It struck him as strange, since the description of the suspect was extremely vague. 'Black-hair' and 'blue eyes' didn't narrow the search on the database either. It seemed that this kid, whoever he was, was going to get away with assault on a member of Legion society.