"Now, here's the thing about gorillas. They are the sweetest animals around. If you leave them alone they will mostly just sit and eat leaves all day. [...] See, now that I was in that gorilla body, I weighed four hundred pounds. And I was mighty strong. How strong? Let me put it this way. Compared to a gorilla, a human being is made out of toothpicks. I wasn't just twice as strong as a man, I was maybe four, five, six times stronger."
"I mean, I'm not the biggest guy in the world. I'm kind of short. I'm kind of small. But when I do this morph I am so massively powerful it's incredible. In this morph I have lifted guys up and thrown them through the air. In this morph I have punched Hork-Bajir and they stayed punched. In this morph I could kick the butts of the entire Dallas Cowboys all at once. Four hundred pounds, give or take a few. But not four hundred pounds of fat. No. I was becoming four hundred pounds of hard-core, bad-as-bad-can-be, don't-even-look-cross-eyed-at-me, shoulders like a cement truck, neck like a fire hydrant, fists like sledgehammers, dominant male Silverback gorilla. Sweet, gentle animals... unless you insist on making them mad. At which point they are capable of ripping up a small tree by the roots and playing baseball - with you as the ball."
The gorilla is Marco's main battle morph. It is also Marco's favorite and most used morph. This morph has been used in most of the battles. There have only been a few times he has used his secondary battle morph wolf. It is his strongest and most used morph. In The Ultimate it is implied that one of the Auxiliary Animorphs acquired this morph.