Madame Web is a character from Marvel Comics that appeared in Ultimate Spider-Man, voiced by Cree Summer. She was Nick Fury's secret asset and has been protected by him ever since Hydra took over the Tri Carrier. As it turns out, she has been with Nick Fury and Nova ever since they went missing.
Role in the series
When Crossbones and HYDRA infiltrate the Inhuman city of Atarog and hold Fury hostage, Madame Web sends Nova to get Spider-Man. Spider-Man and Triton arrive at the city and find Madame Web there, where she explains who she is to the two and helps them find Fury along with Crossbones and several HYDRA agents. Crossbones demand that Spider-Man and Triton turn over Madame Web or else they will kill Nick Fury. Thanks to some planning by Spider-Man and probabilities given by Madame Web, the heroes rescue Fury and repel Crossbones and the HYDRA Agents. Once outside the city, Madame Web departs with Fury to an unknown location for the time being, but also informs Spider-Man and Triton that there is a 99% chance they will obtain another way home. That prediction comes true when the Inhuman Royal Family arrives after they leave.
Later Madame Web summons Spider-Man and Kid Arachnid to K'un-Lun. There she uses the combined mystic energies of the hidden city with the magic of Doctor Strange to open a portal in the Web of Reality. She uses the portal to send the two Spider-Men back to the Spider-Verse in order for them to hunt for the fragments of the Siege Perilous that they had shattered earlier.