Harlan Nelson was a full member of the Mongrels MC who died of lung cancer before the outbreak. He is only mentioned, but you can visit his grave at Pioneer Cemetery.
Alvarez
Alvarez is a drifter who once rode with Deacon and Boozer and did supply runs for the camps. She teams up with Leon to steal drugs from Tucker's Hot Springs camp. You run into her during the opening Chasing Leon storyline.
Leon
Leon is a drifter and thief with a bounty on his head for stealing drugs from Tucker's Hot Springs camp. Deacon and Boozer chase him through the Cascade wilderness in the opening Chasing Leon storyline. He ran supplies between camps alongside Alvarez and Roach.