John Hopkins

And as he honed his skills, he began passing on the knowledge he acquired to others.

After retiring from the army at the age of 40, Don was able to focus on his true passion.

He moved to South Africa and set up a diver training center in a flooded, multi-level mine named Kamati Springs.

For divers, it's a paradise of flooded passageways, deep shafts, and old mine workings.

Together with his wife André, Don has built a thriving business.

Among his specialties is his pioneering use of rebreathers, machines which recycle the gas breathed by a diver instead of expelling it into the water like more traditional open-circuit systems.

Rebreathers allow divers to remain at greater depths for longer periods of time, without needing to carry numerous large gas cylinders.

However, due to the contraption's complexity, there is greater potential for malfunctions.

Still, for Don, this tech is liberating.

Don's reputation as an instructor quickly spread.

Among those drawn to his dive center was Australian pilot Dave Shaw.

Although relatively new to the activity, Dave has already completed a number of impressive dives by the time he visited Komati Springs in September 2002.

And what he lacked in experience, he more than made up for in ambition and ability.

During Don and Dave's first dive together, it was clear this was the beginning of something special.

As their time in the water together increased, so too did their friendship.

A deep, almost brotherly bond soon formed between the two men.

They even looked similar enough that they were frequently mistaken for siblings.

Crucially, they were equals in the water, able to dive together to extreme depths where few could follow.

It wasn't long before Don knew Dave was ready to tackle something more challenging than Kamati Springs.

And in June 2004, they visited Bushman's Hole together.