Aunt May

May Parker is a character from Marvel Comics. May is Peter Parker's aunt and the widow of Ben Parker. She became the sole legal guardian of Peter after the deaths of his parents and her husband, who was shot by a crook that Peter did not stop. She is often seen as a mother-figure to Peter and cares deeply for him, making it difficult for Peter to hide the fact that he's Spider-Man.

Aunt May was created by Stan Lee and Steve Ditko.

Ultimate Spider-Man
Aunt May is a recurring character in the Ultimate Spider-Man TV series, voiced by Misty Lee.

Like her Ultimate comic book counterpart, this version of Aunt May is considerably younger and less frail than her traditional portrayal. She is shown to be involved in various hobbies such as yoga and cooking classes, which allow Peter to sneak out of the house without arousing suspicion. In "Attack of the Beetle", she was asked out to dinner by S.H.I.E.L.D. Agent Phil Coulson (who Nick Fury assigned to be the acting principal of Peter's school). Near the end of Season 3, she reveals she has always known that Peter was Spider-Man, but despite her knowing, she thinks that nothing has changed between them.

Marvel Cinematic Universe
Aunt May is a recurring character in the Marvel Cinematic Universe, beginning with Captain America: Civil War. Here, she is portrayed by Marisa Tomei.

In Civil War, she is visited by Tony Stark, who is looking to recruit Peter under the pretense of a grant. In a post-credits scene, she tends to Peter's injuries, unaware of his dual identity.

Aunt May also appears in Spider-Man: Homecoming, where she acts as a major source in Peter's life. She is concerned about the crimes Spider-Man foils being close to their home. She comforts him after he loses his "Stark Internship" and later helps him when he acquires a date for the homecoming dance. At the end of the film, she finds Peter wearing his Spider-Man suit and reacts in shock.

Trivia

 * The Marvel Cinematic Universe version of May is the third portrayal of the character in Marvel's cinematic history. May was previously portrayed by Rosemary Harris and Sally Field in Sony's two Spider-Man film series.
 * Marisa Tomei has previously acted alongside Robert Downey, Jr. in the film Only You. This may possibly be the reason why Tony Stark is attracted to her, as a call back to that film.
 * Tomei's casting, at her early 50s, was criticized as fans believed she was too young and attractive to play Aunt May. Kevin Feige has stated that being in her 50s makes her realistically old enough to be Peter's aunt, as most of her incarnations are in their elderly years.