According to Charles Smith, both Callander brothers were rather wild and violent men. Similarly Hosea Matthews at one point mentions, that once, when the gang got into some minor trouble in a town named Deer Creek, "Mac went crazy, threatened to kill the whole town".
Uncle at one point can be overheard telling a story of how he once saw Mac single-handed beat up fifteen sailors in a brawl.
A comment by Bill Williamson in a conversation with Uncle indicates that Mac, while he may have seemed at the surface to be a brutal ruffian, in reality was a much more layered and complex person: Williamson tries to express that complexity by describing Mac with the seemingly contradictory formula that Mac was "a heartless son of a bitch, but he had a heart".
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.
- Mac Callander is one of only two members of the Van der Linde gang who does not have a grave that can be found in the game's world (the other being Molly O'Shea).
- The surname "Callander" implies that Davey and Mac may have Scottish heritage.
- "A more vicious pair of bastards there never was." Charles in "The King's Son"
- https://www.youtube.com/watch?v=ooGAc0NCHoA&ab_channel=GTASeriesVideos at 2:31 runtime.
- https://www.youtube.com/watch?v=pNPUnk3cgGc Bill and Uncle talking about Mac Callander - YouTube