Spider-Man has been around in movies longer than almost anyone in the Marvel Cinematic Universe. He has had three Sony movies directed by Sam Raimi, two in the Amazing Spider-Man franchise, and a third MCU movie coming in December 2021. Through them all, Spider-Man has had a pretty consistent supporting cast that all played differing roles in his rise as a superhero.
In the three series, Spider-Man had three different love interests and two different best friends who turned evil against him. He also had loved ones that taught him about responsibility, and an antagonistic newsman who made his life a living hell. Finally, he had two men who stepped up to be the role models he always needed.
Flash Thompson
In the comics, Flash Thompson played a huge role in Peter Parker's rise from nerd to hero. However, in the movies, two versions of Flash were nothing more than a cameo and the third was as different as he can get from the comic book version.
In Spider-Man and Amazing Spider-Man, Flash was the bully he was in the comics, but had no depth and was gone after Peter stood up to him. In the MCU movies, Flash played a much more important role, less a jock bully and more just another geek who picked on Peter, but never really out of spite.
J. Jonah Jameson
Much like Flash Thompson, J. Jonah Jameson never played as important a role as he did in the comics. In the books, JJJ was hugely important and was almost more of an antagonist than any villain that Spider-Man fought on the streets.
Sony did get the casting right, with J.K. Simmons fitting the role of JJJ perfectly. He also made his return in the Spider-Man: Far From Home end-credit scene, and he might become more relevant, but for now, he ranks low on Spider-Man's supporting cast list when it comes to significance.
Uncle Ben
Uncle Ben is the man who taught Spider-Man that, with great power comes great responsibility. However, in the movies, he only really mattered as a man who died and left Peter feeling guilty. In the first Spider-Man movie, Uncle Ben died and passed on the lesson to Peter.
In Spider-Man 3, the memories of Uncle Ben returned. This was because of Sandman's role in his death, something that pushed Spider-Man into a dark time of his life. The lasting memories of Uncle Ben makes him more important than people like Jameson and Flash, but not as important as others in Peter's life.
MJ
From the look of it, MJ might end up as a much more important Spider-Man supporting character in Spider-Man: No Way Home, but after her first two appearances, she is still a minor player and is not as important as any other love interest in the franchise.
In the first MCU movie, she barely played a role and wasn't even the girl that Peter Parker was trying to date. She stepped up in Spider-Man: Far From Home, but that was just one movie of her helping Peter, and she needs to do a lot more to eclipse people like Gwen and Mary Jane.
Gwen Stacy
Gwen Stacy could have been one of the most important characters in Spider-Man movie history. She had the same fate she did in the comics, with Gwen Stacy dying at the hands of the Green Goblin, in a fall that Spider-Man not only failed to stop, but helped make worse.
However, outside of feeling terrible and mourning her death, the films ended without finishing the story and Gwen's death was just another tragic moment, this one unfulfilled for Spider-Man.
Happy Hogan
Happy Hogan was one of Iron Man's most important supporting characters, one of his best friends and most loyal allies. However, with becoming Iron Man such an important mentor for Spider-Man, when he died, it was important for someone to step in to help Peter when he needed an adult to offer him advice and help.
Happy Hogan became that man. While he wasn't interested in dealing with Spider-Man while Iron Man was alive, Peter won him over and he has become an important part of his life, someone that Spider-Man can turn to for help when the need arises.
Mary Jane Watson
Mary Jane Watson was the main love interest for the first three Spider-Man movies and was the most important pure love interest for Peter Parker. She was there from the first movie as the person who gave Spider-Man someone to fight for, and she offered him the proof that he could be loved.
Mary Jane played a vital role as a supporting character in every movie, and she was an essential part of the Harry Osborn storyline as well, with Peter's best friend eventually turning to the dark side. Mary Jane might be one of the best romantic partners in any superhero movie to date.
Tony Stark/Iron Man
Tony Stark is the man who brought Spider-Man to the MCU. When the Civil War movie shook up the Avengers, Tony asked Spider-Man to fight on his side. It was the first time that anyone showed Peter that he was more than just a street-level hero.
Spider-Man and Iron Man worked together until Tony died fighting Thanos. However, it was in the Spider-Man: Homecoming that he showed his true worth as a mentor and father figure. Spider-Man: Far From Home showed how important Tony was to Spider-Man, as he struggled to move on without Iron Man after his death.
Ned Leeds
Every superhero needs his man in a chair, and for Spider-Man, that would be his best friend, Ned Leeds. He was the first person that Peter trusted with his secret identity, and he was there to help him every step of the way.
In the second movie, Ned was still his closest friend and companion and worked with Spider-Man as he tried to figure out who was planning out the attacks while traveling abroad. Whether Ned remains a constant in Spider-Man's life after No Way Home or not, he remains one of the best supporting characters in any Spider-Man movie.
Aunt May
There is really no question of who is the most important supporting character in Spider-Man's movies. That would be his Aunt May. She was there to care for him in Sam Raimi's movies, and the two of them relied on each other after Uncle Ben's death.
She played a lesser role in the Amazing Spider-Man movies, but she was still there to give him a mouthful when he needed it. In the MCU, May is even more important, as it's the only time she knew Peter was Spider-Man, and she was ensuring that he was there to do the right thing while supporting him every step of the way.