Marco Diaz is the deuteragonist of Star vs. the Forces of Evil. He is the teenage son of Mr. Diaz and Mrs. Diaz, as well as Star Butterfly's best friend on Earth.
Marco is at a medium height with tan skin, dark brown hair, dark brown eyes, and a small mole beside his right eye. He wears a light gray shirt, a red zip-up hoodie jacket, dark gray jeans, and brown and white sneakers. He is 14 years old.
Marco is kind and supportive. He has a reputation at his school for being the "safe kid" due to avoiding danger and being cautious, though he insists that he is a "misunderstood bad boy". Although he is not used to the kind of craziness that Star brings into his life, he admits that he would like a little danger in his life and finds fun in fighting monsters with karate. He can get frustrated and/or annoyed with others, such as with Star when she intrudes upon his life.