Darcy Lewis is scientist-geek and a no-nonsense girl whom works together with other scientists Jane Foster and Erik Selvig. She has only appeared in the Marvel Cinematic Universe and it's comic adaptions and has yet to make an appearance in the Main Marvel Universe.
Darcy Lewis first appeared in the movie Thor, where she was played by the actress Kat Dennings. Dennings reprised her role in the second movie, Thor: The Dark World. She also appeared in the Marvel Cinematic Universe comics, but hasn't appeared in any other media or the mainstream comic books yet.
Darcy Lewis worked together with colleagues Jane Foster and Erik Selvig and was one of the first mortals to meet the Asgardian God, Thor. She was instantely atracted to Thor, but nonetheless remained her casual self and helped him and Jane and Erik to defeat Thor's evil half-brother Loki.
Thor: The Dark World (2013)
Darcy was seen again some months after the big fight with Loki. She still worked with both Jane and Erik and discovered the teleportational holes that led to the defeat of Thor's newest advisory, Malakith the Accursed.