The term ONE FIGHTING AGAINST THANOS is an AVENGER, a team of superheroes in the Marvel Cinematic Universe. The AVENGER in question is Iron Man, a billionaire industrialist and genius inventor played by Robert Downey Jr. Iron Man is one of the founding members of the Avengers and has been a major part of the team since its inception. He is known for his bravery and willingness to fight against Thanos, the powerful villain from the Marvel Cinematic Universe.