The most iconic one-day endurance event in the world will bring together a highly regarded and competitive professional field of triathlon athletes. 

Lange will be seeking his second win in Kailua-Kona, where he holds a course-best time of 8 hours 1min 40sec from his win last year, as well as the marathon run-course best time of 2:39:45, set in 2016 when he finished third.

Also competing for the title is Canada's Lionel Sanders, who led the 2017 race through mile 23 of the marathon before giving way to Lange and ultimately ending up second.

Germany's Sebastian Kienle, the 2014 world champion, will be looking for another title after just missing out on the podium last year.

Great Britain's David McNamee, meanwhile, will look to follow in the footsteps of Lange and move from a third-place finish to becoming a world champion the following year.

The women's field will be striving to de-throne three-time world champion Ryf, who continues to add to her impressive resume.

In addition to earning her fourth Ironman 70.3 World Championship title in South Africa last month, the Swiss also claimed victories at the Ironman European Championship in Frankfurt in Germany and Ironman 70.3 in Gdynia in Poland.

Also likely to be in contention will be last year's other podium finishers, Lucy Charles of Britain and Sarah Crowley of Australia.

Furthermore, there will be the highly-anticipated return of three-time Ironman world champion Mirinda Carfrae of Australia.

The 2018 Ironman World Championships will offer a total professional prize purse of $650,000 (£494,000/€562,000) which will be distributed to the male and female athletes finishing from first down to 10th.

It also marks the 40th anniversary of the original Ironman event.

"This is a monumental year for Ironman as we celebrate four decades of racing at the Ironman World Championship in Hawaii," Andrew Messick, President and chief executive of Ironman, said.

"We look forward not only to honouring the historic professional performances from years past, but also showcasing the ever-growing international triathlete talent that will be on full display."