Mary J. Blige had acted professionally before her Golden Globe-nominated turn in Dee Rees’ “Mudbound,” appearing opposite Tom Cruise in the hair-metal musical “Rock of Ages” in 2012, channeling the Wicked Witch of the West as Evillene in a live production of “The Wiz.” She even played Dr. Betty Shabazz, Malcolm X’s wife, opposite Angela Bassett in the TV movie “Betty & Coretta.” Yet even though Rees had only seen her in “The Wiz,” she knew the unproven actress would be perfect to play the weathered Florence. Below, she explains why.
Had you seen Blige act before you cast her in the role of Florence?
I saw her do “The Wiz” live — I grew up on [the original film] and I have the  album with Diana Ross and Nipsey Russell. For her to take on [the role of Evillene, the wicked witch] was huge and risky, and there was a fearlessness in her performance: She wasn’t self-conscious or caring about the audience or any known interpretation of the role. She remade Evillene.
You’ve said you knew she would bring empathy and vulnerability to the role of Florence. Did she bring any qualities you didn’t expect?
She also brought a lot of strength and a knowingness. She was able as Florence to have this kind of stoicism and experience pain and fear and disappointment, but not let it touch the loved ones around her. [Blige] is such a strong, serious woman who is able to hold many things, and she’s such a serious actress: She’s on set early, knows all her lines and everybody else’s lines, and she’s completely willing to let go of ego and vanity and be stripped down — and that’s amazing for someone who’s an icon. And she invested a lot of trust in me as a director, and because of that we were able to go deeper and make her character very layered and complicated.
Was forcing her to not wear makeup and wigs part of your psychology in making her embody the character?
In some ways yes, because I wanted her to be completely free, and not worry about anybody’s expectations — to let her know, “You’re not Mary, you’re Florence.” I think it’s freeing in that way. For her as an actress is probably takes more work, because she’s so known. She has more to work against in terms of getting into character. The craft, deliberation, thinking and restraint Mary employs when she’s working … it’s not easy, and she makes it look effortless. I’m so proud of her.
How long have you been a fan of her music?
Oh god, since I was a kid! Even in college [Blige’s 1994 sophomore album] “My Life” was like a soundtrack for people growing up in the ’90s. The emotional landscape of relationships — the hopes, the disappointments, the insecurity — she sings about in an unvarnished, “this is what’s really happening inside of me” way. She went beyond the romance, candles and the veneer [of] what we thought it was supposed to look like, and showed us the corners and the edges and the things that hurt. She connects with her audience because she relives stories for you — she’s not just singing at you. It’s like therapy.
Did you have any input into “Mighty River,” the Golden Globe-nominated theme song for the film that Blige wrote with longtime collaborator Raphael Saadiq and Taura Latrice Stinson?
No! I just wanted her to write from the heart. I was hesitant to ask her [to write a song for the film], because I didn’t want her to think that I [was after] her music and not her sheer acting talent. So I waited a long time, and then [“Mudbound”] got into Sundance and I finally asked [her manager], “Would Mary ever think about doing a song?” He was like, “Oh my God, she’s been waiting for you to ask!” “Mighty River” is more than I could even imagine.