A maths professor who made headlines as the first person to swim around Bermuda turned his account of the feat, and the colourful life leading up to it, into a fundraiser for charity.

Seán O’Connell’s gruelling, record-setting swim, inspired by a pub bet, led to US open-water swimmer Lori King beating his record 40 years later in 2016.

A legacy was set when the challenge got taken up again two years later by another swimmer, Sarah Eismann, a New Yorker.

As Dr O’Connell recounted in his 2017 book, Shark Bait, the idea sprang from an impulsive claim over beers at the Robin Hood Pub when a friend, Vince Dawber, called his bluff and bet him $1,000 that it could not be done.

“Swimming around Bermuda became the only thing on my mind,” Dr O’Connell wrote, likening his preparation to his PhD thesis in mathematics — start with simple cases and “build up gradually to the very complicated”.

From August 21 to 23, 1976, over 43 hours and 27 minutes, Dr O’Connell beat the odds in a swim featured in The Guinness Book of Records that raised thousands of dollars for the Bermuda Physically Handicapped Association.

Dr O’Connell was born in the Flatbush neighbourhood of Brooklyn, New York, the only child to strict Irish Catholic parents. He recalled his upbringing as “so rigid as to be inconceivable today”.

He trained to become a Jesuit priest after high school, then opted for teaching as a career instead.

Dr O’Connell credited his Jesuit experience with giving him the mental stamina for his challenge in Bermuda.

He wrote: “The sacred silence practised for many years in this religious order proved to be highly effective training for the lonely silence of the long-distance swimmer.”

After teaching in Britain, Dr O’Connell spotted an adverrtisement for a job at the Bermuda College and moved to the island in 1974.

His link to the BPHA came courtesy of the late activist Margaret Carter, secretary of the association, who approached him after he gave a talk about his proposed swim.

They decided to use it as a fundraiser. Dr O’Connell became treasurer of the charity and ultimately raised more than $65,000 for the cause.

His first attempt to circle Bermuda was unsuccessful, but six weeks later, exhausted but elated, he came ashore after a swim of 37.5 miles.

The first-time feat made Sports Illustrated, followed by the 1978 Guinness Book of World Records, and a history volume on open-water marathon swimming.

Dr O’Connell went on to challenge himself further, including a round-the-island run in 1979 and pushing wheelchairs on the same perimeter route two years later for the BPHA.

A 30th-anniversary challenge with the Bermuda Masters Swimming Association, in which a relay of swimmers circles the island, brought in $30,000 for charity.

The 1976 swim, however, sealed his reputation in Bermuda.

“Why did I do it?” Dr O’Connell wrote in his memoir.

“Of course, the initial trigger was the money Vince offered as a powerful incentive. Forty years ago, $1,000 was a small fortune, particularly for a person like myself just starting life as a Bermuda College lecturer.

“Coming right on the heels of this was the elegance of the exploit, an idea of compelling beauty to me, particularly since it had never been done before.

“There are few things in life worth pursuing that have not already been achieved by someone else.”

Dr O’Connell is survived by his wife, Celia.

• Seán Kevin O’Connell, a longstanding lecturer at the Bermuda College, was born on April 20, 1942. He died on July 11, 2023, aged 81