MacKenzie "Big Mac" Chalker, better known to his friends and colleagues simply as Mac, is a former health care assistant who worked at Holby City Hospital's emergency department from 2007 until 2016. He was initially a porter upon his arrival in the department in November 2007 but later trained to become a emergency care assistant for extra money in 2013. In 2014, he retrained to become a health care assistant and work back in the ED following Jeff Collier's death. In 2016, he resigned following an incident with some stolen drugs which left him feeling guilty.