In a joint interview, the actor and writer discuss “The Last Days of Ptolemy Grey,” their “fairy tale” about an old man negotiating dementia and family drama with the help of a wonder drug.Samuel L. Jackson made his name in the movies, Walter Mosley in literature. But when it was time for these two arts legends to collaborate, they knew television was the only medium that would work.“The Last Days of Ptolemy Grey,” a new limited series starring Jackson and written by Mosley, based on his 2010 novel, tells the story of an elderly Atlanta man with dementia and a family that wants his savings. Just when it looks like all Ptolemy has left is to count his remaining days, two people alter the course of his life. One is Robyn (Dominique Fishback), a teenage family friend who decides Ptolemy is worth taking care of. The other is a neurologist (Walton Goggins) working on a new drug that will bring back Ptolemy’s cognizance — but only for a short time, after which he’ll be worse off than ever (shades of the Daniel Keyes novel “Flowers for Algernon” and its film adaptation, “Charly”).In the series, Jackson’s title character reclaims his life with the help of a young caretaker played by Dominique Fishback.Hopper Stone/Apple TV+In his newfound lucidity, Ptolemy comes to terms with events and people from his past, including the one true love of his life, a beauty named Sensia (Cynthia Kaye McWilliams), and Coydog (Damon Gupton), a childhood mentor who left behind an unusual inheritance. As these figures come and go from his mind, Ptolemy also takes it upon himself to solve the murder of a beloved nephew (Omar Benson Miller), a task appropriate to Mosley’s bread-and-butter turf of crime fiction.Jackson and Mosley were also executive producers on the series, which premieres Friday on Apple TV+. The project was personal for both of them: Each has had loved ones who suffered from dementia. During a freewheeling video interview — Jackson was in London (where he’s filming the Marvel mini-series “Secret Invasion”), Mosley in Los Angeles — they discussed the fairy tale quality of “Ptolemy,” why television was the best option for the project, and how the story jumped across the country from Los Angeles to Atlanta, among other subjects. These are edited excerpts from the conversation.“It’s a fairy tale,” Jackson said of his new series. “In reality, there is no cure for Alzheimer’s or dementia, but we get one, however momentarily.”Erik Carter for The New York TimesWho is Ptolemy Grey?WALTER MOSLEY He’s all of us everywhere. This is a destination that either we reach ourselves in our own experience, or with people that we know and love and live with, as far as aging, dementia and death. These things impact everybody’s lives. It’s a great thing to have Sam taking it on and bringing it to a neighborhood that other people don’t seem to think about very much.SAMUEL L. JACKSON As based in reality as we want it to be, he’s actually at the center of a fable. He’s this mythical character that Walter created who has a real-life problem at the beginning, but Walter allows us to circle back and see a life well lived. It’s a fairy tale. In reality, there is no cure for Alzheimer’s or dementia, but we get one, however momentarily, that allows him to be clear about everything that’s happened in his life, in a flash.How does the series address the experience of dementia?MOSLEY A lot of people will see somebody who’s experiencing dementia or Alzheimer’s, and they think, ‘They’re crazy.’ But in reality, there’s something really going on in there, no matter how far gone they are. We allow an audience to identify not only with the character that Sam’s playing, but with our own lives. That was what the book meant to me, to be able to do that.JACKSON Those of us who have had to deal with that know that when those people are sitting there, they may not answer your questions or be present for what you want them to be present for, because they’re busy inhabiting something else that gives them solace in the lost space that they’re in, or that we think they’re in. But they may not be lost at all. They just don’t bother with what you are trying to put on.I talked to my mom when she had dementia and she’d be like, “You’re disturbing me. Stop asking me things that I’m supposed to know the answer to, or you think that I know the answer to, or that I don’t want to be engaged in right now.” When she wanted to engage, she engaged. So this story touched me in a real place.“This is a destination that either we reach ourselves in our own experience, or with people that we know and love and live with, as far as aging, dementia and death,” Mosley said.Erik Carter for The New York TimesAnd through the story, you get to invent a cure, albeit a temporary one.MOSLEY That’s the great thing about imaginative creativity. You look at Jules Verne: He’s the guy who invented the [electric] submarine, who invented the rocket to the moon. He invented all of this stuff in his imagination, and of course, it’s stuff we wanted. I was reading the newspaper yesterday, and they said umbilical cord stem cells have cured a woman of AIDS. This one woman is cured, and they did it from umbilical cord stem cells. If you put the possibility out there, lots of people are going to be thinking about it.Walter, you’ve worked in television quite a bit by now, including as an executive producer on the crime drama “Snowfall.” Sam, you have mostly stuck to movies. What made TV the right medium to tell the story of Ptolemy?MOSLEY Television has the potential to do some amazing things that are good for drama, good for actors, and good for an audience to be able to understand and identify with characters who have real arcs of change. We’re coming up on our final season of “Snowfall,” and we’re going to get to see how things are going to work out or fall apart. That’s what’s been fun.JACKSON There’s a great satisfaction for me to have a character development that allows an audience to go back and say, “OK, that’s where he started. Oh, that’s why he’s this guy. Oh, that’s why he treats women this way.” We watched movies for a very long time before we realized something like “Roots” could come along and be a mini-series. All of a sudden, boom, there’s “Roots,” and you go, “[expletive], that’s the way to tell the story.”The novel takes place in Los Angeles, but the series takes place in Atlanta. Why the move?JACKSON Georgia has better tax breaks.MOSLEY Yes, it wasn’t feasible to do it in L.A. First, we were going to go to Atlanta and try to make Atlanta look like L.A. But Atlanta doesn’t look like L.A.JACKSON There’s not one palm tree in Atlanta.Did setting the series in Atlanta add anything thematically?JACKSON There are certain elements of Atlanta that are historically indigenous to telling a story like this. Anybody who’s lived in any place that’s full of Black people will recognize this. How many white people are in this story? There’s the doctor, and the nurse. A lot of people are going to look at this and go, “Where are the white people?” You didn’t encounter them unless you had to when I was growing up in the South. In Atlanta, they had Black insurance companies, they had Black newspapers. Everything you needed, you could get in the Black community. You didn’t have to go outside of it.MOSLEY I really do think that all of those things are trace elements that impacted the making of the series, with the actors and the crew just being in Atlanta. We would tell the story anywhere we were, but making it in Atlanta was in itself an experience, and that experience had to impart some of its history to the series.Let’s talk a little about the collaboration between you two. Walter, why was it important to have Sam onboard for this?MOSLEY Sam is a great actor, but that’s just a very small part of the answer to your question. I wrote the book 13 years ago. Sam knew the book better than I did. He’d say, “No, no. Don’t you remember? You did this,” and I’d say, “Oh, yeah. OK.” He’s also an executive producer, and his commitment to the book and getting it made is why we got it made. When I was shopping it, people would say, “Sam Jackson doesn’t do television.” Well you’re right, but he’s going to do this. His commitment to it, his talent in doing it, his willingness to play a very different kind of role than he usually does and to make that work so beautifully — it was really great.Sam, what is it about Walter’s work that pulls you in?JACKSON Walter is a very feet-on-the-ground kind of guy that understands and knows his characters and knows the environment that those characters are in. Environment is very important when you’re a reader. I read a lot, two or three books at a time. Descriptions and character development are very important things, no matter what, and Walter has a command of those things that a lot of writers don’t. I read bad novels along with good ones, but I always know that I’m going to get something very satisfying when I’m reading a Walter Mosley book. More