The people behind the work -- Entertainers like Elvis Presley and Bill Cosby often get uncredited help hitting those high notes or penning best-sellers

Elvis fans from Tupelo to Las Vegas say they’ve seen his ghost. But perhaps stranger than any tale of the resurrected King is the fact that Elvis had a real, live ”ghost” while he was still very much in the flesh. In his last year, the increasingly sickly Presley hired pure-voiced tenor Shaun Nielsen to tour with him and invisibly hit those high, drawn-out notes the King himself could no longer command.

”I could see he was sick,” recalls Nielsen, ”but you know, you didn’t want to say, ‘Elvis, you’re fat.’ I mean, you loved the guy.” So when Elvis was having an off night onstage and something tricky such as ”Now or Never” or ”American Trilogy” came along, Nielsen would ”double” him, singing along with — and sometimes in place of — Elvis. ”It was like if he wanted to let go, he knew there was someone there holding it for him,” explains Nielsen. Once Elvis had had a chance to catch his breath, he would quit lip-synching and start singing for real again, and the crowd would never suspect. On the 1977 live recording of ”Unchained Melody,” the voice you hear on the last four high notes is Nielsen’s, dubbed over Elvis’.

If Nielsen’s role as a ghost singer was a bit unusual, he has plenty of counterparts in the other arts: writers who ghost other people’s prose, artists who ghost others’ images, actors who ghost others’ voices. The famous often walk hand in hand with unknown phantoms, and sometimes it’s impossible to tell which one is real. In fact, since Elvis’ time, technology has greatly increased the chances of blending the work of talented unknowns with that of big names — just when the commercial value of fame has hit an all-time high.

Because of the high stakes involved, more and more ghosts are coming out of the ectoplasmic closet, often accompanied by their attorneys. Yvette Marine is suing Virgin Records for a million dollars in royalties, claiming that she ghosted lead vocals for wispy-voiced Paula Abdul on Forever Your Girl. Martha Wash, the voluminous veteran of the singing group the Weather Girls, charged that her vocals on the Black Box hit ”Everybody Everybody” were attributed to slinky fashion model Katrin Quinol. Wash sued Black Box distributor RCA Records; they settled out of court. Wash also sang the famous hook ”Everybody dance now!” for the C+C Music Factory hit ”Gonna Make You Sweat,” though in the video, C+C singer/sex goddess Zelma Davis lip-synchs the line.

Ghost singing (or writing or performing) shouldn’t be confused with perfectly legitimate artistic collaborations. By the same token, nobody would criticize a celebrity who uses and credits a hired-gun writer, as in the new memoir Take My Life, Please! by ”Henny Youngman with Neal Karlen” or I Remember by ”Dan Rather with Peter Wyden” — though nobody can say whose words are whose. Collaborations become controversial when the hidden party isn’t credited. ”It’s a simple matter of integrity,” says Robert Silvers, coeditor of The New York Review of Books. ”Concealment is unfortunate on the simple grounds that people should know the truth.”

Matters get especially sticky when the work in question goes on to win a prestigious award. The late Jerzy Kozinski omitted from his novels any acknowledgment of assistance; a 1982 Village Voice article alleged that assistants had written important chunks of Kozinski’s fiction, a charge two of the assistants later denied.

One case of uncredited collaboration on award-winning work actually appears in America’s newspapers every day. Virtually no one knows it, but the hand that has been drawing Doonesbury for the past 20 years belongs not to the hermetic Garry Trudeau but to Kansas City-based artist Don Carlton. Carlton stresses that he generates none of the words or basic ideas for the strip, but the final drawings in the Pulitzer Prize winner all come from his pen.

”I take Garry’s pencil roughs, and I redraw them in pen and ink,” Carlton says. ”No tracing is involved I do all his lettering, too. Everything you see I have done, but not without his guidance.”

The two artists met in 1971, 11 months after the strip began national syndication. Carlton was a 34-year-old magazine circulation manager in Kansas City. The 23-year-old Trudeau was headed off to grad school at Yale and needed help meeting his deadlines. ”In the early days, the strip was a bit more brittle and harsh,” says Carlton. ”It has a different look now — more free, and less static.”

Each Friday, Carlton rises at 7 a.m. to find sketches Trudeau has faxed from New York. By 5:30 p.m., Carlton takes a week’s worth of comics to the production department at Universal Press Syndicate. Trudeau rarely sees the strips before he opens his newspaper.

While such renowned comic artists as Al Capp and Chester Gould had assistants draw backgrounds and secondary characters in Li’l Abner and Dick Tracy, Carlton’s arrangement is evidently unique. ”I’m the only one I know who does this,” he admits. ”Most cartoons are done totally by the person who signs them.” Carlton also does the covers of Doonesbury books and the new catalog offering such Doonesbury merchandise as Uncle Duke’s bomber jackets, and he illustrates (but doesn’t write) Trudeau’s op-ed columns for The New York Times. ”I enjoy the process without ever feeling any ego needs for credit,” he says.

Like poltergeists in haunted houses, ghosts sometimes twinkle in and out of the visible spectrum. Ralph Schoenstein was the uncredited ghost of Bill Cosby’s mega-best-sellers Fatherhood and Time Flies. Schoenstein acknowledges writing the Cosby books. But it wasn’t until Love and Marriage and the recently published Childhood that Schoenstein’s contribution to all four books was formally recognized by Cosby.

The Schoenstein-Cosby collaboration is unusual. It begins with the two sitting around while Cosby ”free associates” about his life. Schoenstein offers reminiscences of his own, and a tape recorder takes it all in. ”Then I go home and turn it into prose,” says Schoenstein. So whose work is it anyway? According to Schoenstein, he and Cosby are ”identical. We had the same boyhoods. He was poorer. But he’s not anymore!”

Schoenstein apparently doesn’t resent not getting initial credit for the first two books, even though Harvard prof Alvin Poussaint got big cover listings for all four of his introductions. At one time Schoenstein was irritated by the disparity between his original five-figure fee and Fatherhood‘s millions in sales. But his fee has risen with each book. He won’t comment on that or say whether he got any bonuses from Cos, but something has made him a friendlier ghost.

Sometimes, just as in a traditional spook story, death can beget the ghost. After best-selling horror novelist V.C. Andrews (Flowers in the Attic) died in 1986, her books kept coming; her publisher, Pocket Books, says that Andrews’ posthumous work is based on story lines and ideas she simply didn’t have time to flesh out. Now her novels are being ghosted by teen-horror novelist Andrew Neiderman — and some readers have written the publisher to say that the Andrews books seem to be getting better. One thing is for sure: As long as big money is involved, art will never give up the ghost.