If you happened to be a teenager in the late 1960s or early ’70s, Harlan Ellison was a literary giant. The prolific, pugilistic writer transformed geeky science fiction into mind-blowing prose, becoming a point man for a new generation of fabulists bursting free of the genre’s pulpy conventions to go where no one in the field had gone before.

Mr. Ellison, now 74, wasn’t the only important author rewiring sci-fi to more deeply explore social, psychological, metaphysical, and ethical themes, nor perhaps the most cultishly lionized (Philip K. Dick takes the prize, as might, to varying degrees, Samuel Delany, Ursula K. Le Guin, or the mysterious James Tiptree Jr.). But he was the loudest, the angriest, and the most abundantly published in every available medium, from magazine short stories to acutely memorable episodes of “Star Trek” and “The Outer Limits.”

“Dreams With Sharp Teeth,” Erik Nelson’s documentary opening tomorrow at Film Forum, is utterly agog at Mr. Ellison’s larger-than-life persona, but knowingly so. This is not a standard biography with old television clips, talking-head interviews, and historical montages — although it has all of those things. What Mr. Nelson takes advantage of, and also indulges, is Mr. Ellison’s hammy streak. He gives the writer generous face time to blast off on all his favorite topics: the abuse of writers, the stupidity of Hollywood, the cruelty of his fellow man, and, most of all, Harlan Ellison.

Between flashbacks to the author’s scrappy childhood in Cleveland, where the diminutive Mr. Ellison learned to outwit bullies, and clips of the flinty firebrand sparring with Tom Snyder on “Tomorrow,” Mr. Ellison offers a guided tour of his life.

Much of it appears to have been spent behind his typewriter, which bears the legend, “I am an artist and should be exempt from s—.” The comment is attributed to the pop singer P.J. Proby, but is far more fitting for Mr. Ellison, who, when not reinventing science fiction or (reportedly) bedding hundreds of women during his lean, mean heyday, often was engaged in legal battles to assert just that point. Mr. Ellison nearly went bankrupt suing AOL, but often enough has scored more than Pyrrhic victories, as when he won acknowledgment from the producer James Cameron for having written two pieces that inspired “The Terminator.”

Mr. Nelson, who began shooting Mr. Ellison for a different project in 1981, decided to pursue a full-blown documentary in 2002, and the long arc serves the film extremely well. The contrast between the younger, lady-killing hotshot and the mellower, silver-haired septuagenarian he is today is fascinating in that age has not blunted his crankiness, though it has softened him into more of a sweetheart beneath the combative veneer.

Mr. Nelson does not so much frame his subject within the history of pulp fiction (he first pursued his profession cranking out 3,000-word stories for a penny a word in New York in 1955), or vintage TV, or the culture of fantasy fandom, as label him a one-man cultural phenomena. “He’s like a skin graft on a leper,” says Robin Williams, an old pal who shows up at the house. But Mr. Ellison outperforms the comedian, giving short dramatic readings from pieces such as “Repent, Harlequin! Said the Tick-Tock Man,” and his teleplay for “The City on the Edge of Forever,” seemingly everyone’s favorite “Star Trek” episode. Curiously, Mr. Nelson decided to augment these colorful performances with badly executed computer-graphic backdrops that make for an odd distraction.

What’s also curious, given Mr. Ellison’s many legal entanglements and five marriages, is that Mr. Nelson never summons anyone who might offer something more than a sympathetic anecdote. There’s lots of footage of Mr. Ellison screaming at (or about) other people, some of whom have become close friends after surviving the crucible of his scrutiny. But there’s not an instance of anyone screaming back. Still, given Mr. Ellison’s volatility, he conjures a tornado of talk that makes most secondary comments redundant. Early on, someone describes the writer as an unlikely confluence of borscht and Berkeley. That unabashed blend of showmanship and fierce free speech not only makes Mr. Ellison a valuable cultural iconoclast — it makes “Dreams With Sharp Teeth” great entertainment.

Through June 10 (209 W. Houston St., between Sixth Avenue and Varick Street, 212-727-8110).