Donnie is an associate and friend of Butchie's, who plays a role as hired muscle at Butchie's request. While in County Holding during season 4 (on false charges of murder) Omar is assisted by Donnie and a friend who provide Omar with body armor made from thick, large books - Omar is attacked in holding by a man who attempts to stab him. Omar is able to subdue the man and stab him in the rectum, sending a message to the other inmates not to attempt any other attacks.
In season 5, while enacting his vengeance against the Stansfield organization for Butchie's murder (done purposely by Chris Partlow to draw Omar out of hiding), Donnie stakes out Monk Metcalf's apartment building with Omar, waiting for a chance to move on Monk. Donnie and Omar assault the apartment and are ambushed by Partlow and Snoop. Donnie is killed when Partlow shoots him in the head, killing him instantly.
Donnie is played by Larry "Donnie" Andrews. Andrews' real-life Baltimore exploits were the inspiration for the character of Omar Little.