Rushton Skakel Sr.

Rushton Skakel Sr., brother of Ethel Kennedy and head of a family business that was once one of the largest private companies in the country, died Thursday. He was 79.

Mr. Skakel, whose son, Michael, was convicted in June of a 1975 murder, died in Hobe Sound, Fla., after a long battle with a brain illness, his lawyer, Emanuel Margolis, said early yesterday.

Margolis said Mr. Skakel developed frontal lobe dementia.

Michael Skakel ' s trial lawyer, Michael Sherman, said, " In the four years that I ' ve had contact with him, he ' s always been in failing health, both mentally and physically. It ' s a very tragic ending. "

Rushton Skakel was one of seven children born to George and Ann Skakel. His sister, Ethel, married future Attorney General and Sen. Robert F. Kennedy Jr. in 1950. Robert Kennedy was assassinated in 1968.

Rushton Skakel took over the family business, Great Lakes Carbon, in the mid-1960s, after the deaths of his parents and brother, George Skakel Jr., in separate plane crashes.

The company, which manufactured carbon coke, was once one of the largest private companies in the country.

That wealth was on display in the Tudor-style mansion in the Belle Haven section of Greenwich, Conn., where Rushton Skakel and his wife, Anne Reynolds Skakel, raised their seven children. Anne Reynolds Skakel died of cancer in 1972 at the age of 42.

In 1975, a neighbor of the Skakels ' , 15-year-old Martha Moxley, was beaten to death with a golf club, later identified as belonging to a set owned by the Skakel family.

Michael Skakel was charged with murder in January 2000. He was sentenced in August to 20 years to life in prison. He is appealing the conviction.