Hubert J. “Hub” Schlafly Jr., a television engineer who aided countless politicians and performers when he helped invent the scrolling public-speaking crutch known as a teleprompter, died April 20 of undisclosed causes at a hospital in Stamford, Conn. He was 91.

Inspiration for the teleprompter came in the late 1940s from a Broadway actor, Fred Barton, who dreamed up a device that would help him remember his lines. He pitched his idea to Irving Kahn, then vice president for radio and television at 20th Century Fox.

Kahn turned to Mr. Schlafly, director of television research at Fox.

“I said it was a piece of cake,” Mr. Schlafly told the Stamford Advocate newspaper in 2008.

He installed a motorized scroll of paper inside half a suitcase. Actors’ lines were printed on the paper in half-inch letters, and the suitcase was set up next to studio cameras. The scrolling speed was controlled by a stagehand.

“We tried at one time to have the speaker control the speed,” Mr. Schlafly told the Advocate. That idea went nowhere, he said. “It was like patting your head and rubbing your stomach.”

Gambling that they would find customers for their invention, Barton, Kahn and Mr. Schlafly quit their jobs to start a new company, TelePrompTer Corp.

They introduced the device in 1950 on the CBS soap opera “The First Hundred Years,” and it soon became a standard accouterment for live broadcasts, such as “The Tonight Show” and “The Ed Sullivan Show.”

The company’s breakthrough came in 1952, when former president Herbert Hoover inaugurated the teleprompter as a politicians’ tool in a speech before the Republican National Convention. At one point, Hoover interrupted his script to improvise. When the teleprompter paused, Hoover panicked and, under his breath, urged that the scrolling resume.

The moment was observed by hundreds of reporters, and their stories served as free advertising. “We must have gotten 10,000 newspaper clippings from around the world about Hoover using the prompter,” Mr. Schlafly once recalled. “That got us into the public- speaking business.”

TelePrompTer Corp. served as a consultant to at least five political conventions. The company developed an all-in-one convention podium, which came with a prompter, plumbing to deliver drinking water and an elevator to give shorter speakers a lift.

Refining the prompter concept, the company eventually replaced the conspicuous suitcase unit with glass panels placed on either side of the speaker — a familiar sight to anyone who’s watched a State of the Union address in recent decades.

Later, the company’s Lens Line Prompting System superimposed words in front of the camera, allowing a speaker to look directly into the lens while reading a speech.

In ensuing decades, others refined and updated the teleprompter concept, developing computerized text and software that scrolls automatically at the speed of a speaker’s sentences.

TelePrompTer, meanwhile, branched out into the nascent cable television business. By 1970, it had become the country’s largest cable company.

Mr. Schlafly, then TelePromp­Ter’s vice president, helped overcome many of the burgeoning industry’s technological hurdles. He did fundamental work with Hughes Aircraft on a now-prevalent method of broadcasting across rivers, mountains or city streets without physically laying cable.

In 1973, Mr. Schlafly demonstrated the future of television when he helped secure use of a Canadian satellite to broadcast images from Washington — including footage of House Speaker Carl Albert — to the National Cable Television Association’s convention in Anaheim, Calif.

It was the first coast-to-coast satellite transmission of television images, and trade journals heralded it as a significant moment in TV history.

But for all the promise of satellite distribution, logistical problems prevented it from catching on immediately. And TelePrompTer — mired in legal and financial trouble and after Kahn, the chief executive, was convicted in 1971 of bribing government officials while bidding on a cable franchise — decided not to pursue it.

Mr. Schlafly left the company and continued to push for the development of satellite transmission as an independent consultant. In 1975, he helped engineer HBO’s satellite transmission of the “Thrilla in Manila” boxing match between Joe Frazier and Muhammad Ali — a landmark broadcast that succeeded in demonstrating satellite TV’s vast economic potential.

Hubert Joseph Schlafly Jr. was born in St. Louis on Aug. 14, 1919, and moved frequently as a boy as his wildcatter father chased oil. He graduated from the University of Notre Dame with a degree in electrical engineering in 1941.

Mr. Schlafly was an engineer for General Electric and the Massachusetts Institute of Technology, where he worked on radar technology for the war effort before joining Fox in 1947.

In his later career, he was president of Transponder Corp., a telecommunications company, and of Portel Services Network, a communications patent-licensing concern. He retired in 1998.

His wife of 59 years, Leona Martin Schlafly, died in 2003. He had no immediate survivors.

Mr. Schlafly received two Emmy Awards for his technical achievements — one in 1992 for his work developing cable systems and another in 1999 for his part in developing the original teleprompter.

In 2008, he was inducted into the Cable Television Hall of Fame at a ceremony in Denver. He delivered his acceptance speech with the help of a teleprompter — his first occasion to use the device, he told the audience.