In the Marvel Cinematic Universe, one would find the most commercially successful actors from Hollywood, mainly the ones who played the heroes, such as Chris Evans, Robert Downey Jr, Chris Hemsworth, late actor Chadwick Boseman to name a few.
The Avengers franchise has elevated Marvel superheroes to new heights, but what has retained our interest in them and who actually make them the heroes? It is the bad guys.
None of the Avengers superheroes would have been what they are today without the compelling motivation to bring their enemies down. Loki came with a strong back story, and without him, there wouldn't have been any Avengers.
Thor would have remained in Asgard, Captain America in the ice, Iron Man would have remained famous for his contribution in America's defence section, and the Black Panther wouldn't have bothered to align Wakanda with the outer world.
With viewers, Loki has had a complicated love-hate relationship. He has always been seen as a villain by Thor and company, (sometimes unfairly), and has never really belonged...in any planet, circle. Not even in Asgard.
Time and again he was always reminded that he was not an Asgardian, and his identity was always to remain under the shadow of his popular brother, Thor, (who back then did not have the best of ideas about being the ruler of the world).
Even in a game of 'Get help', he had to play the victim. In the team of Avengers, Loki has been treated as nothing less than a bad tool.
But Marvel keeps bringing him back, even after giving him a heroic death, in Avengers: Infinity War. The God of Mischief managed to play his last trick in Avengers: Endgame. To the Avengers, he will remain a mass murderer, but only we know what he really meant to the entire film franchise.