The Collector is the exterminator from the beginning of the movie. He collects people that he finds interesting and keeps them in the red box. After Arkin is in the ambulance on his way to the hospital when a van crashes into the ambulance. The collector kills the drive and takes Arkin.
After the credits the collector is watching a slide show while sitting on the box. Arkin is yelling hes going to kill him once he gets out and the collector kicks the box to shut him up
Thanks Greg H!