- "I, a descendant of slaves, am asking you to show humanity!"
- ―MacDonald to Caesar
MacDonald was the personal assistant to Governor Breck in the fourth movie, and a descendant of slaves who, ironically, commanded slave apes (although he had a different attitude towards the apes, instead of the usual bossiness his master role was decent and even-handed) including Caesar, who was planning an ape revolt. MacDonald did not believe that Caesar was the son of the talking apes Cornelius and Zira, or that Caesar was capable of speech – until Caesar admitted otherwise. He did not support Breck's policies towards the apes but was also wary of what the apes rebellion would lead to. He was friendly to Caesar, who saw McDonald's race as a reason for him to empathise with the apes.
First giving Caesar the chance to escape when the authorities were onto him, then sabotaging the electroshock table Caesar was placed on to force him to speak, MacDonald helped Caesar to launch his revolt – which turned into a night of fires and carnage, as apes around the city turned on their masters. He then took Caesar on verbally at the movie's end, when Caesar wanted to fully punish humanity for its treatment of apes. Being descended from slaves, McDonald implored Ceasar to follow the example of his ancestors and show humanity for their former masters, lest the revolution devolve into anarchy and barbarism.
In Battle for the Planet of the Apes (which took place 27 years after the events of Conquest), Malcolm's younger brother (also referred to as "MacDonald") was Caesar's human liaison and advisor, and spoke with his authority around Ape City. With both MacDonalds playing virtually the same role toward Caesar, how one came to be exchanged for the other is never explained on-screen.
- The short story The King Is Dead - Long Live the King, written by Rich Handley for the anthology Planet of the Apes: Tales from the Forbidden Zone, reveals that Malcolm MacDonald had been shot by Kolp during an attempt to assassinate Caesar.
- Early scripts for Battle for the Planet of the Apes again featured MacDonald, but actor Hari Rhodes wasn't available for filming at the time. Instead, the part was given to Austin Stoker, playing MacDonald's younger brother. One script included MacDonald's line: "when the bomb dropped on the city and Caesar heard of my brother's death he said 'my heart is torn.'"
- Marvel Comics' adaptation of Battle for the Planet of the Apes was based on the early scripts of that movie (writer Doug Moench claimed to have not seen the later Apes movies that he adapted to comic format), and consequently featured MacDonald as the same character who appeared in Conquest. Here, he was given the full name 'Bruce ('Mac') MacDonald'. Uniquely, Marvel also published an original story set between Conquest and Battle which detailed how MacDonald and the loyal humans were given their freedom from slavery after the group of slaves led by former Governor Breck rebelled and fled to the destroyed city.
- MR Comics' Revolution on the Planet of the Apes comics detailed the aftermath of the events of Conquest. Here, MacDonald was given the full name "Malcolm MacDonald".
- Conquest of the Planet of the Apes
- Conquest of the Planet of the Apes (novel)
- Planet of the Apes Magazine: Conquest of the Planet of the Apes
- Planet of the Apes Magazine: Quest for the Planet of the Apes
- Planet of the Apes Magazine: Battle for the Planet of the Apes
- Revolution on the Planet of the Apes