Private Addison is one of the most prolific members of the so-called Barracks 3 gang - those who support Hogan and his men in their operations. He can be seen in almost every episode, usually doing something in the background. He has full knowledge of the doings of Hogan and his men, and has helped them on many occasions. Addison has even appeared at least once in German uniform as a camp guard, although neither Klink nor Schultz seemed to have noticed.
Addison is a close friend of Private Broughton and at one point shared a bunk with him in Barracks 2. Toward the end of the series, though, he sleeps on the top bunk directly across from the barracks door. Most of the time, during roll calls, you can see him standing beside Broughton, directly behind LeBeau.
Addison's main character trait seems to be silence. He has no speaking parts in any episodes (unlike Broughton). The few times we do see him speaking, he is usually too far away to make out what he is saying. Does have a speaking part in Episode 9, Season 2, with the mini radio operated tanks. He yells 'Geronimo' down the main tunnel entrance in the barracks.
Addison is first named during mail call in Request Permission to Escape. then again in Drums Along the Dusseldorf, and again during roll call in The Big Dish.