Species: Human
He is Jake's best friend and they have been since they were younger.
Marco's dad is Peter, who does engineering and night maintenance. His mother, Eva, was controlled by Visser One until she was freed near the end of the series. Her death was faked prior to the start of the series as a way to get her off the planet. (It appeared that she had drowned.) His father was a normal human who was clueless of this fact.
Morphs
His most-used battle morph was a gorilla.