Mister Aer is a light globe research and manufacturer who lives in Welltower. His son is also named Aer. Generally, when the books refer to the father, he is called Mister Aer; the son is called Aer.
Mister Aer is a cruel man who does not tolerate failure well. He is a genius inventor, but he likes to ruthlessly test dangerous technology on terrified involuntary assistants.
He sells his technology to both Alizon and, secretly, Serrin.
At one point he finds Kaehl and Selda and delays them until guards arrived to capture them.
Mister Aer lived a relatively rich life inside Welltower inventing and testing technologies until the events of the flood, when he was kidnapped by Serrin to build them a missile guidance system. He was quickly rescued by Alizon troops. He then defended Alizon City using their light globes as a shield.
After that he was sent to prison for years of collusion with Serrin. He remained there, conducting research, for 21 years until Aer convinced Longiver to let him out.