This is Blackout from Agents Of S.H.I.E.L.D., he was a one off villain towards the end of Season 1, he stalked a Cellist Coulson had a thing going with before his first death, who was mentioned in The Avengers, and he tried to kill her, the team stopped him.

Anyways, the actor was in Captain Marvel, and Victoria Alonso heavily implied that it's the same character, so he's the first character originally from a Marvel Television project, to be in a Marvel Studios project. Again, this was in Captain Marvel, so before any of the following returned in these projects:

* Edwin Jarvis (Agent Carter > Avengers: Endgame)
* Daredevil (Daredevil, Defenders > Spider-Man: No Way Home)
* Kingpin (Daredevil > Hawkeye)
* Black Bolt (Inhumans > Doctor Strange In The Multiverse Of Madness; might be a variant)
* Daredevil Supporting Cast + Punisher + Jessica Jones (Netflix Shows > Daredevil: Born Again)

tl;dr: A one-off AoS villain was the first Marvel Television character to be in a Marvel Studios project.
How is he the first Marvel Television character to make it into a Marvel Studios project?