|Family||Sgt. Lilley - Daughter|
|First Appearance||"Warren's Dream"|
|Last Appearance||"The Vanishing"|
|Death Episode||"The Vanishing"|
|Cause of Death||Bitten by Sgt. Czarnecki. Out of mercy by Sgt. Lily|
|Series lifespan||"Warren's Dream" to "The Vanishing"|
Nothing is known about Lt. Mueller prior to the apocalypse, other than that he was part of the US military. He has a daughter named Lilley.
Lt. Mueller is seen consoling refugees at the camp.
During a search for the missing convoy, the group come under attack. Lt Mueller is forced to give the mercy order on his friend. However it doesn't kill him, and the group flees the attack.
Sgt. Czarnecki is found by Lt. Mueller. Mueller shoots Czarnecki in the head, thinking he has given mercy to him. Mueller is incorrect and Czarnecki is seen getting up in the background, and Mueller is killed off-screen. He later returns to the camp as a zombie attacking the group. He is then killed permanently by Pvt. Lilley