Robert A. Maheu, a chief aide to Howard Hughes who engineered the deals for the Hughes business empire that helped change the face of Las Vegas but who never once met his boss in the decade and a half he worked for him, died Monday in Las Vegas. He was 90.

United Press International

Robert A. Maheu, in 1974.

The cause was congestive heart failure, his son Peter told The Associated Press.

Communicating with Hughes through countless handwritten messages and phone calls, Mr. Maheu bought a host of Las Vegas hotels and casinos and other real estate in and around the city for Hughes in the late 1960s. Those deals, adding a corporate presence to a city with a reputation for mob influence, were arranged while Hughes was secluded at the Desert Inn in Las Vegas, seen only by a few aides and doctors.

“If Howard wanted someone fired, I did the firing,” Mr. Maheu recalled in his memoir, “Next to Hughes,” written with Richard Hack. “If he wanted something negotiated, I did the bargaining. I was his eyes, his ears and his mouthpiece. I met with presidents, appeared before committees and entertained the rich and famous.”

Mr. Maheu was remembered as well for his involvement in an affair going far beyond the bizarre world of Hughes, the billionaire businessman, movie producer and aviator turned recluse. In 1960, Mr. Maheu was enlisted by the C.I.A. in a plot to have the underworld carry out the assassination of Fidel Castro.

Mr. Maheu’s roots were far from the glittering world of wealth and power he ultimately entered. He was born and reared in the mill town of Waterville, Me., the son of French-Canadians. His father owned a grocery store.

He received a bachelor’s degree in economics from Holy Cross College in 1940, then became an agent in the Federal Bureau of Investigation. He told of working in counterintelligence in World War II and trapping a couple of Nazi agents who had arrived in New York City.

He left the bureau in 1947, worked for the Small Business Administration, and in 1954 founded Robert A. Maheu and Associates, an investigative agency. He soon began working on retainer for the Central Intelligence Agency, as he told it, capitalizing on his friendships with former F.B.I. agents who worked for the agency.

In July 1975, Mr. Maheu told the Select Committee on Intelligence in the Senate that the agency had asked him in 1960 to meet with Johnny Roselli, a Mafia figure, to help hatch a plot to assassinate Castro. Mr. Maheu said he took the assignment without pay, out of a sense of patriotism, and later went to Miami, meeting with Mr. Roselli and other mob figures as a prelude to having the Mafia arrange for someone to slip poison into Mr. Castro’s food.

In June 2007, the C.I.A. confirmed the outlines of the plot in releasing excerpts from a 1973 internal report detailing activities it had undertaken that might not have been authorized by its charter. After several failed efforts to poison Mr. Castro, the plot was abandoned after the Bay of Pigs invasion, the agency said.

Mr. Maheu had begun working for Hughes in 1954, quashing a blackmail plot against him as one of his first assignments. In 1957, as Mr. Maheu recalled it, Hughes, then living in the Bahamas, asked “if I would be his alter ego.”

As Mr. Maheu told KNPR Radio in Las Vegas long afterward, “He pointed out to me that he had decided never to make another public appearance, never to appear before a Congressional committee or a regulatory body, and that it was up to me to come up with a plan whereby when people spoke to me, they in fact were speaking to Howard Hughes.”

But Mr. Maheu eventually clashed with a rival group of aides to Hughes and was stunned when Hughes secretly left Las Vegas in November 1970, going to the Bahamas. Mr. Maheu was fired soon afterward, and in 1972, in a telephone news conference to expose as a hoax a supposed autobiographical collaboration with Clifford Irving, Hughes denounced Mr. Maheu, saying, “He stole me blind.”

Mr. Maheu won a $2.8 million defamation judgment, but it was overturned. A settlement, its terms undisclosed, was later reached. Hughes died in 1976.

Mr. Maheu was involved in his own various business ventures after leaving Hughes.

In addition to his son Peter, he is survived by his sons Bill and Robert; 10 grandchildren; and six great-grandchildren, The Las Vegas Sun reported. His wife, Yvette, died before him.

Mr. Maheu basked in Hughes’s mysterious aura in buying all those hotels and casinos.

“He was, in effect, the King of Vegas,” Mr. Maheu said in his memoir. “And as his surrogate, I wore the crown.”

Robert A Maheu