Master Chief from T3H Metroid Galaxy
Master Chief Petty Officer SPARTAN-117, whose birth name is John but is most commonly referred to as the Master Chief, is a main character of the series. He is the protagonist of the Halo series, and appears as part of a crossover with Metroid.
In his original cameo appearance in the Anniversary Special, Master Chief wears realistic SPARTAN armor despite the fact that the the Red vs. Blue characters, who also wear that armor, only have this realistic armor in their own universe, and are stick figures with Samus-esque helmets in the TMG universe. In the actual series, Master Chief is a combination of his appearance in the Anniversary Special and the appearances of the Red vs. Blue characters, a stick figure with a SPARTAN-style helmet.
Master Chief initially fights Samus before the two team up to stop the Covenant from unearthing the Ark and activating the Halos. He seemingly sacrifices himself by crashing a Covenant capital ship into the Ark, but the secret scene at the end of the season reveals he is still alive. He later saves Samus from the lava of the volcano and helps in the massive war.