Marco Lopez is a failed hybrid, but not because he cannot do everything his hybridization promised.

Marco's change went too far for him to be disguised as still human when his DNA was joined with that of a lemur.

Marco has a lemur's large bright eyes, but his most distinguishing characteristic is a large tail for balance. Marco can scale anything. If he can get a grip, he can climb it.

To Marco's embarrassment, he has also taken on the scenting characteristics of a lemur. Flowers are also especially tasty to Marco, so anyone who sets out blooming plants around the facility knows to warn Marco to keep away (although if the flowers have a strong scent, good luck there).

By design, Marco continues to evolve, with his face and body taking on a more lemur-like form as time passes. Marco has set himself a challenge: to stop marking the research facility with his scent. He doesn't know if he can be successful, but he vows to try.

We first meet Marco in Book 2 of The Human-Hybrid Project, Inside the Darkness.