By Richard Sandomir

New York Times News Service

Stanton T. Friedman, whose conviction that extraterrestrials have arrived on Earth led him to leave his career as a nuclear physicist to lecture widely about alien visitations, died May 13 in Toronto. He was 84.

His family said he died of a heart attack at Toronto Pearson Airport on his way home to Fredericton, New Brunswick, from a speaking engagement in Columbus, Ohio.

Friedman had worked for major corporations on projects like rockets and compact nuclear plants for space when he left the world of established science to become a prominent voice in the study of unidentified flying objects, or ufology, a field embraced by many but viewed by many more with skepticism.

“He was the ideal person for the role because he was a nuclear physicist, a rocket scientist — a genius — but he spoke the people’s language, and he didn’t put himself on a pedestal,” Kathleen Marden, one of Friedman’s co-authors, said in a telephone interview. Their book, “Captured! The Betty and Barney Hill UFO Experience” (2007), chronicled her aunt and uncle’s supposed close encounter with aliens.

In several books, many television appearances and hundreds of speeches around the world, Friedman demonstrated little doubt that alien spaceships had come and gone, and that extraterrestrials had walked the Earth.

“What this means,” he told The New York Times in 1987, “is that we humans are not the big shots we think we are.”