While he was enrolled in the Gunpla Academy, Julian usually gave his opponent a lecture during Gunpla Battles to point out the flaws in their Gunpla so they could improve upon it. Such an example occurs during his fight against the GPB-X80DE Beginning Evolution, during which he tells the pilot (a Saki Mishima lookalike) that while its MA mode was fast, its maneuverability was lacking and thus made it easy to predict its movement. Julian then attacked the MA parts and forced the Beginning Evolution to land in its MS mode. He paused briefly to allow his opponent to prepare a counterattack, noting that, being based on GPB-X80 Beginning Gundam, the Gunpla's true strength was surely close combat and he wanted to see it. Tatsuya Yuuki, who observed the battle, noted that despite losing to Julian, the opponent would learn something, and since both fighters gave their all, there wouldn't be any hard feelings afterward.
Outside of Gunpla Battle, Julian is friendly with a dash of humor, and described by Tatsuya as a "reliable senior".
Originally from Manchester, England, Julian was one of Tatsuya Yuuki's seniors at the Gunpla Academy. He originally enrolled at the age of 15, and within four months had become the head of the class. By age 18 he had accrued an unofficial record of 204 wins and 3 losses, and was viewed as a potential successor to the second Meijin Kawaguchi. However, after seeing the Meijin's ruthless tactics and belief that victory was all that mattered, he became disillusioned with the title. He subsequently withdrew from both the academy and Gunpla Battle in general to protect his love of Gunpla.
At the time of the 7th Gunpla Battle World Championship, his grandfather Sir John Ayers Mackenzie was a competitor in the semi-finals of the tournament. Seeking to rekindle Julian's interest in Gunpla Battle, Sir Mackenzie pretended to be dying, and requested Julian take his place in the tournament as his "dying" wish. In the process, he reunited Julian with the Gunpla he used at the academy - the Gundam F91 Imagine.
Julian obliged, and faced his former classmate, now the third Meijin, in Gunpla Battle. As they fought, he demanded Tatsuya show him his beliefs and determination. When he found all his attacks were met, and that his fighting style wasn't ruthless, like the second Meijin's, he accepted Tatsuya as the new Meijin, and admitted he couldn't stay away from Gunpla Battle any longer.
It's revealed in Hobby Hobby Imaging Builders volume 20 that he uses V2 Gundam Imagine Fullburnern in the 8th Gunpla Battle World Championship. Volume 37 shows that he also used another Gunpla, the Gundam M91, in the same competition.
- He shares his surname with that of Christina Mackenzie, Rusty Mackenzie and his grandfather, John Ayers Mackenzie.