T'Challa a.k.a. Black Panther is now officially part of the Marvel Cinematic Universe, after having made his (by all accounts, triumphant) debut in the MCU in Captain America: Civil War. Chadwick Boseman will return as T'Challa for his own solo movie in 2018, with Creed writer/director Ryan Coogler calling the shots from a script that he's co-writing alongside screenwriter Joe Robert Cole (a graduate of Marvel Studios' old in-house writers program).
Other Marvel Comics characters with key ties to T'Challa's home nation of Wakanda have likewise appeared in MCU films now. That includes frequent Black Panther antagonist Ulysses Klaue (Andy Serkis) - who appeared in Avengers: Age of Ultron - and Everett K. Ross (played by Martin Freeman in Civil War), a diplomat who has worked with T'Challa on political matters in the Marvel Comics universe.
It remains to be seen if either Serkis and/or Freeman reprise their MCU roles during Coogler's film (though Freeman seems hopeful that it will happen). Meanwhile, THR is reporting that Lupita Nyong'o has now entered talks to join the Black Panther movie cast, as a (for now, under-wraps) love interest for T'Challa.
The Oscar-winning star of 12 Years a Slave is already a member of the Disney (and affiliates) family, having also played the motion-capture rendered alien Maz Kanata in Star Wars: The Force Awakens (a role she will reprise in Star Wars: Episode VIII) and Mowgli's adopted wolf-mom Raksha in director Jon Favreau's The Jungle Book. Nyong'o is costarring in Disney's upcoming true story-based inspirational drama Queen of Katwe on top of all that, so it seems all the more likely that she will sign on for Black Panther too.
Perhaps T'Challa's most famous love interest from the Marvel Comics Universe is that of Ororo Munroe a.k.a. the X-Men team member Storm, with whom he even had a son named Azari. The fact that the X-Men film rights lie with 20th Century Fox and not Marvel Studios means that Storm - neither the Halle Berry version nor the younger version played by Alexandra Shipp in X-Men: Apocalypse - won't be becoming the Queen of Wakanda during Coogler's film, nor will she be played by Nyong'o or anyone else in the MCU anytime soon.
However, one strong possibility for Nyong'o's potential role in Black Panther is that of Monica Lynne, a singer who actually saved T'Challa from being killed (during their first encounter) and was his longtime love interest in the world of Marvel Comics. Another character that Nyong'o could potentially end up playing here is a member of the Dora Milaje: the personal bodyguards of the Black Panther and Wakandan women who, as part of an ancient Wakandan tribal tradition, are selected as potential queens for an unmarried Wakandan king (like T'Challa in the MCU). Either way, the hope is that the Black Panther movie role is well-written and worthy of Nyong'o's acting talents.
Captain America: Civil War is in theaters now. Doctor Strange opens November 4, 2016; Guardians of the Galaxy Vol. 2 – May 5, 2017; Spider-Man: Homecoming – July 7, 2017; Thor: Ragnarok – November 3, 2017; Black Panther – February 16, 2018; Avengers: Infinity War Part 1 – May 4, 2018; Ant-Man and the Wasp – July 6, 2018; Captain Marvel– March 8, 2019; Avengers: Infinity War Part 2– May 3, 2019; and as-yet untitled Marvel movies on July 12, 2019, and on May 1, July 10, and November 6 in 2020.