Assuming the frequently-delayed film arrives as scheduled, this should be a good primer. As Leto explains in the video, "Morbius first appeared as an antagonist in The Amazing Spider-Man in 1971, and eventually evolved into more of an anti-hero. For years, Marvel was actually forbidden [by the Comics Code] from using characters considered more on the supernatural side. So it was a really big deal when Morbius finally made his debut.
"He was part of a much darker turn within Marvel," the actor, who also brought DC's the Joker to life in Suicide Squad and the Snyder Cut of Justice League. "One that fortunately fans fully embraced. After all, everyone loves a good monster story. There's something that stoked people's imagination that really can grab a hold of you. It certainly did with me. See you in theaters!"
In the film, Leto plays Dr. Michael Morbius who, through experimentation to cure a rare ailment, finds himself transformed into a vampire who thirsts for blood, but whose human self fights against it. Matt Smith is Loxias Crown, a friend of Morbius' who suffers from the same disease; Adria Arjona is scientist and Morbius' fiancee Martine Bancroft; Jared Harris is a professor that is also Morbius' mentor; Tyrese Gibson is FBI agent Simon Stroud, who is hunting Morbus; and, unless his part has been cut for some reason, Michael Keaton will be back as Adrian Toomes (aka Vulture) from Spider-Man: Homecoming, which would suggest that that particular Spider-Man shares the universe with Morbius. Then, again, given the events of Spider-Man: No Way Home, who knows?
Look for Morbius on April 1.