Texan Sallie Ann Clarke, known as the authority on the legendary Lake Worth Monster, has died at the age of 80, one of her children said.

Clarke wrote a 1969 book about the Lake Worth Monster, a 7-foot-tall man-goat creature allegedly first seen near the Texas lake that year.

Clarke, who claimed to have seen the Lake Worth Monster on three occasions after penning her book, said in a 1989 interview that her experiences with the creature made her regret her book's tone.

"If I'd seen it before I wrote the book, the book would have been quite a lot different," she said. "It wouldn't have been semi-fiction. It would have been like a history."

Clarke's husband, Richard Lederer, said while some dismissed the Lake Worth Monster as a teenage prank, his wife remained a true believer.

"She offered a $5,000 reward for any person who could pass a polygraph that they were the monster," Lederer said.

The Fort Worth (Texas) Star-Telegram reported Saturday that Clarke, who died of unspecified causes Tuesday following a long illness, is survived by Lederer, three children, six grandchildren and two great-grandchildren.