Darcel MacArthur, better known by his nickname "Big Mack", is the official leader of the Loose Cannons, a group of teenagers who found themselves on the run after being kidnapped and experimented upon by a mysterious group.
On March 7, 2007, Darcel and eleven other students were removed from school under false pretenses and subjected to an experiment intended to create Dynamorphs—in the process turning the kids into Dyna-Hosts and changing the genders of a few of them. Before there was a chance to extract the dynamorphs from the test subjects, however, they managed to escape.
Even before the transformation, Darcel was a big black young man. Afterwards, he became more handsome and muscular, but still keeping some resemblance of his previous appearance.
Big Mack received something similar to "PK Superman" package. When using his powers, he is limned with a pale blue glow, and becomes much stronger, tougher and able to fly.