Russell is a burned out drug addict.
Russell was intorrogated by Hank Schrader and Steven Gomez over his possession of a bag of Blue Sky meth. Hank pressed him on who sold him the meth at a bar, as Russell had given him vague details -- which included the man having tan pants and Russell being 80% sure that he had a moustache. Russell finally remembered that the man who sold him the meth was named Mel. However, he then said it could've been Mark instead, and that it had a "muh" sound. Frustrated, Hank sarcastically thanked Russell and left with Gomez, intending to go and investigate the bar ("Green Light").