AUSTIN, Texas -- The University of Texas is mourning the loss of Peter Flawn, who was twice the president of the university and one of its most distinguished leaders.

The university said Flawn passed away overnight Sunday.

He was 91.

Flawn served as president of the University of Texas at San Antonio from 1973 to 1978, then at UT-Austin from 1979 to 1985, and returned to UT-Austin from 1997-1998 (ad interim).

He was a geologist that helped the campus' transformation into a top public research university in the 1980s.

"Peter was a visionary leader at UT, a beloved friend and a wise counselor to me and many university presidents," said Gregory L. Fenves, president of UT Austin. "Whenever the university sought his help — from his earliest days doing geology research in West Texas through his time as president emeritus — Peter always answered the call. His contributions to our great university were immense and we will miss him deeply."

A memorial services is planned, but details are still being worked out.

"When one looks back at the intellectual giants that led The University of Texas, Peter Flawn's name will be right at the top of the list," said William McRaven, chancellor of The University of Texas System. "Peter was a special person and over the last two years, I developed a deep respect, admiration, and friendship with this wonderful man. He dedicated his life to educating the young men and women at UT Austin, UT San Antonio and throughout the state of Texas. We will miss him dearly."

UT said Flawn was predeceased by his wife of 70 years, Priscilla Pond Flawn, in 2016, and a daughter, Laura B. Flawn, M.D., in 2001.