Mr. Llewellyn, a Harlem-born entrepreneur worth about $170 million, had run companies, served presidents, sat on bank boards and had powerful friends like Bill Cosby and Gen. Colin L. Powell. But at 80 years old and in failing health, he found himself chasing visitors in his wheelchair as they headed for the 10th-floor elevator, his once powerful 6-foot-5 frame struggling to keep up. A fall and other ailments had forced Mr. Llewellyn into rehabilitation, and after several months, his doctors said he was well enough to return to his Central Park West apartment. But his wife of nearly 30 years disagreed, saying he was too ill.