Mary Jane Watson is an important character. She is Peter's love interest and often gets caught up in the dangerous situations that Spider Man has to deal with. Another main character is Aunt May, who raises Peter. She represents the family and moral support in his life. And there are also the villains like the Green Goblin and Doctor Octopus, who play crucial roles in creating the conflicts in the story.
There's also J. Jonah Jameson, the publisher of the Daily Bugle. He is always trying to get pictures of Spider Man and often portrays him in a negative light in the newspaper, which adds an interesting dynamic to the story.