|Behind the scenes|
The Absolute (Mentioned)
When the Animorphs intially entered The Gardens to acquire battle morphs to attack the Yeerk pool, it was Marco who acquired Big Jim. Big Jim was Marco's very first morph, and became his primary battle morph.
Later when the Animorphs began recruiting new members, one of the new recruits also acquired a gorilla morph in the Gardens; it is unknown whether this gorilla is Big Jim or not.
According to Cassie, he and Marco are similar to each other mentally. This explains why Marco had control of his gorilla morph.