When Prince first signed with Warner Bros. Records, he didn't want to be categorized as a black musician. This was the late 1970s, before music by black artists was widely marketed to multiracial audiences; before kids in every household in America were glued to their screens watching "Thriller" on MTV.To avoid being boxed in — which for black artists often meant making less money and reaching smaller audiences than their white counterparts — Prince encouraged rumors about his identity, hinting at being biracial when both his parents were black. In the 1984 movie Purple Rain, Prince's parents are played by an African-American man and a white, Greek woman. The fiction of his racial background endured throughout his career, even creeping into some of last year's obituaries.The way Prince worked to dissolve categories is one of the central themes that Ben Greenman explores in his new book, Dig If You Will The Picture. Greenman said that combining multiple, often conflicting identities, was integral to Prince's work. And race wasn't the only way Prince stirred things up."From very early on, he just shattered ideologies," said Greenman, who has been a Prince fan since middle school in the early eighties. "[His] process was to isolate two theoretically opposed aspects of a self, of a person — male-female, black-white, straight-gay, good-evil. And he played out that opposition in his work. Sometimes he resolved it to his satisfaction; usually he didn't. And the tension between those two things powered the work. That was the engine at the center."That tension resonated with Prince listeners of many different backgrounds. In an article for Time, Touré (who also wrote a book about Prince), wrote that "Prince sits at the edges of race, gender, and sexuality and rejects all borders." He said that in doing so, Prince was almost able to become "a genre unto himself sonically and interpersonally."According to Greenman, multiplicities played out in all sorts of ways — in terms of musical style, fashion, album art, even the members of his bands. Musically, it meant combining different genres, techniques and influences. Sometimes it even meant creating different identities, like his Camille persona, a higher pitched alter ego that he used in the 1987 song "If I Was Your Girlfriend." The song begins with the lyric, "If I was your was your girlfriend would you remember to tell me all the things you forgot when I was your man?"Then there's the 1981 song "Controversy," in which Prince delves into sexuality. In it, he asks, "Am I black or white? Am I straight or gay?" Thirty-five years ago, that was a more fraught question than it might be today. "Playing straight-gay was [a] very important thing for that time, in the eighties, when AIDS was a relatively new major issue," Greenman said. "Here was this guy who was so flamboyant and nobody could really pinpoint or put their finger on his sexuality, and he didn't really clarify."Years later, Prince became a Jehovah's Witness, "and a lot of that early flamboyance and that early dissolution of category went away," Greenman said. "Part of it was that he just got older and his sense of himself, I'm sure, changed. But that early period Prince went to great lengths to blow up everything."In blowing up everything, Prince made space for a new generation of artists. When Prince died in 2016, Frank Ocean posted a tribute acknowledging the ways in which Prince was a trailblazer. "[Prince] was a straight black man who played his first televised set in bikini bottoms and knee-high heeled boots, epic," Ocean wrote. "He made me feel more comfortable with how I identify sexually simply by his display of freedom from and irreverence for obviously archaic ideas like gender conformity."Behind the scenes, Prince was notoriously shy, and he didn't do a lot of interviews. But when he did, he committed hard to the idea that he and his music were not to be put into a box. In a 1999 TV appearance, Larry King expressed confusion at what to call Prince, who at the time was not going by Prince, but an unpronounceable symbol. Later in the conversation, King asked Prince, "How would you describe your music? What idiom would you put it in?"Prince responded: "The only thing I could think of, because I really don't like categories, but the only thing I could think of is inspirational."Greenman said that the way Prince forced fans to reckon with their own notions of identity was a form of subtle activism. Later in life, that propensity to address social injustices became more overt, even as Prince himself tended to speak more conservatively. After he died, fans started learning about the scope of Prince's philanthropy. Van Jones, an activist and commentator on CNN, has talked about the lengths Prince went to support causes he believed in, like green jobs initiatives, and teaching black kids how to code. In an interview with Rolling Stone, Jones said that in 2006, when he was working on George W. Bush's Green Jobs Act, he received an anonymous check for $50,000. Later, he found out the check was from Prince. Prince also made direct reference to social issues in some of his later songs, like 2015's "Baltimore," which talks about the deaths of Michael Brown and Freddie Gray at the hands of police."A lot of the way [Prince] addressed social issues was revolutionary early on, and sort of slogan-based," Greenman said. "He would urge people to educate themselves, or overthrow the existing order, or don't listen to everyone ... It was hard to imagine being a Prince fan in 1984, 85, 86, and not going through that process of reassessing beliefs all the time. Both because as a fan you had to follow him, and because every message was about searching and finding and questioning what you were." Copyright 2017 NPR. To see more, visit http://www.npr.org/.