On Sept. 24, 1950, Jimmy Nelson, a skinny 21-year-old ventriloquist, was introduced by Ed Sullivan on his Sunday night variety show, “Toast of the Town,” as “the greatest I’ve ever seen in his field.”

Mr. Nelson was clean-cut and genial, with an air of boyish mischief. His dummy was a smart aleck in a suit and bow tie.

“My name is Danny O’Day,” the dummy said to the audience. “This schnookle standing next to me is Jimmy Nelson. The kid thinks he’s a ventrickolist.”

“That’s ventriloquist,” Mr. Nelson said, starting a rapid-fire exchange with his dummy.

“Ventrickolist,” Danny said.