He was a long time friend of Richard Webber and was for a long time in search of a liver. Despite being at the top of the transplant list, Mackie didn't feel he would ever get a new liver so he had no problem doing things normally out of character like smoking or acting gay. When he was at Seattle Grace Hospital he told George O'Malley that dying was a get-out-of-jail-free card. He could be as bold as he wanted, and there was nothing anybody could say about it.
He finally received his new liver from Kevin Davidson.
When George was his doctor, he flirted with him often, despite not being gay.
- His room number was 4451.