Steve Forrest for The New York Times
Fans outside the Gielgud Theater in London, where "Equus" is playing.
Daniel Radcliffe appears as a disturbed young man in Peter ." 
Steve Forrest for The New York Times
The actor Daniel Radcliffe signing autographs backstage at the Gielgud Theater. One fan’s opinion: “Wow, he must have been working out.” More Photos >
“We’re all kind of freaked out about seeing his — well, him naked,” Ms. Tobin, 20, said after a recent performance. “I still think of him as an 11-year-old boy.”
To make it clear what audiences are in for, at least in part, photographs of Mr. Radcliffe’s buff torso, stripped almost to the groin, have been used to advertise the production. It is as jarring as if, say, Anne Hathaway suddenly announced that instead of playing sweet-natured princesses and fashion-world ingénues, she wanted to appear onstage as a nude, murderous prostitute.
“Equus” opened last week, and the consensus so far is that Mr. Radcliffe has successfully extricated himself from his cinematic alter ego. Considering that playing Harry Potter is practically all he has done in his career, this is no small achievement.
“I think he’s a really good actor, and I sort of forgot about Harry Potter,” said Ophelia Oates, 14, who saw the play over the weekend. “Anyway, you can’t be Harry Potter forever.”
In The Daily Telegraph, Charles Spencer said that “Daniel Radcliffe brilliantly succeeds in throwing off the mantle of Harry Potter, announcing himself as a thrilling stage actor of unexpected depth and range.”
Mr. Radcliffe told The Telegraph that “I thought it would be a bad idea to wait till the Potter films were all finished to do something else.” There are still a few to go. The fifth, “Harry Potter and the Order of the Phoenix,” is scheduled for release on July 13, and Mr. Radcliffe has signed on for the final two installments as well. (Meanwhile, the seventh and last book in the series, “Harry Potter and the Deathly Hallows,” will hit stores on July 21.)
Harry and Alan could not be more dissimilar as characters, even if both “come from quite weird backgrounds,” as 13-year-old Ella Pitt, another recent theatergoer, put it. (And no, she declared, she was not too young for all the nakedness, swearing and sexuality.) Both characters have unresolved issues relating to their parents: Harry, because his are dead, and Alan, because his have driven him insane.
But when it comes to romance, for instance, the celluloid Harry has yet to kiss a girl; the big moment comes in the forthcoming film. Meanwhile, Alan in “Equus” not only engages in some serious equi-erotic nuzzling with an actor playing a horse, but is also onstage, fully nude, for 10 minutes, during which he nearly has sex with an equally naked young woman.
“Equus,” which also stars Richard Griffiths as the unconventional psychiatrist who helps untangle Alan’s ecstatic madness and tortured imagination, is playing to sellout audiences at the Gielgud Theater here, and there is talk of transferring the production to Broadway, perhaps next season. Some people are drawn by interest in the play itself, which won the Tony Award for best play in 1975. Some come to see Mr. Griffiths, a seasoned actor who himself won a Tony Award last year for his role in “The History Boys.”
Then there are the Radcliffe fans, who have watched the actor negotiate the rocky path of adolescence right before their eyes. They have watched his Harry Potter fly through the air, forget to do his homework, talk to snakes, smite people with his magic wand, stay up past his bedtime and suffer any number of traumatic near-death experiences. Try as they might during the performance, they cannot completely de-Potter their minds.
“I was, like, ‘I don’t want to see him poke the eyes out of horses,’ ” said Marie Aveni, 22.
Emily Bunch, 21, remarked, “I thought, ‘Harry Potter! Where are your glasses?’ ” Wendy Krekeler, 20, described her first glimpse of the shirtless Mr. Radcliffe this way: “I thought, ‘Wow, he must have been working out.’ ”
But, his admirers say, it is clear that Mr. Radcliffe is not a one-trick actor, fated to end his career playing elderly magicians in “Harry Potter” rip-offs.
“I wanted to see if he could play both a wizard boy and a psycho patient,” said Ashley Lucas, 21, “and I think he did an excellent job.”
Mr. Radcliffe’s star presence in “Equus” does not appear to have traumatized innocent “Harry Potter” aficionados, although not everyone knows what to expect. At one performance, Karoline Nordmo, an admirer from Sweden, said she was hoping to buy tickets for herself and her 12-year-old sister, Lorentine.
“We know that it has something to do with horses, and that he’s in it,” she explained.
Katelyn Gill, 20, a student from California who saw “Equus” with several friends, said the experience had not ruined the “Harry Potter” films for her; it only changed her perception of its star.
“After we saw the play, we were like, ‘Oh, my God — we’ll never be able to see Harry Potter in the same way again,’ ” she said. “We saw him naked!”
