Mac and his brother Davey were two criminals who joined Dutch van der Linde's gang at some point in the past. According to Charles Smith, they were both rather violent. Additionally, according to Uncle, Mac once beat up fifteen sailors.
In 1899, the Van der Linde gang attempted to rob a ferry in the town of Blackwater. However, things turned sour and both Callander brothers were injured. Davey was rescued and taken with the gang as they fled for the mountains, although Mac was separated from them and had to escape on his own.
Mac was eventually caught and killed by Agent Milton of the Pinkerton National Detective Agency, who would later claim that Mac was "shot up" by the time they caught him and that his death was “slow but merciful”.
Events of Red Dead Redemption 2
Mac was mentioned several times by Arthur Morgan and other members of the gang, who lament his absence and surmise that Mac died as Davey did.
Horseshoe Overlook Chapter
While fishing with Jack Marston, Arthur is approached by Pinkerton agents Andrew Milton and Edgar Ross, and the former reveals what happened to Mac and uses his death to taunt Arthur. Jack, being too young to have understood the situation at the time, expresses concern for Mac's safety, and Arthur reassures him by saying that Mac might be somewhere safe.
His death would be mourned by the gang members, one of them being Bill Williamson, who fondly says Mac was just the type of man that you'd want to go robbing with.
Beaver Hollow Chapter
When Arthur reveals to Charles that he is sick and dying, Charles tells Arthur that he has the chance to make amends, unlike many of the other gang members, including Mac and Davey, saying that the brothers were a “vicious pair of bastards” and that’s all they ever were and will be.
- Lenny and Charles are the only members of the gang to imply any dislike of the Callander brothers. Every other member of the gang, including Hosea, appears to regret their passing.
- The surname "Callander" implies that Davey and Mac may have Scottish heritage.