Budapest - The swimming world championships starts on Sunday in Budapest with China, who topped the medal table at the 2015 world championships, determined to maintain their dominance.
A young US team led by Katie Ledecky will seek to dislodge them while the competition will throw up mouth-watering duels including the toxic freestyle feud between Australia's Mack Horton and China's Sun Yang.
Here are FIVE big names to look out for over the coming days:
The pressure will be on 25-year-old Chinese giant when he again locks horn with Australia's Mack Horton in the men's 400m freestyle on Sunday - dubbed the "War in the Water II".
Horton, 21, dethroned Sun over 400m at the 2016 Rio de Janeiro Olympics, having called his rival a 'drug cheat' in the build-up, a remark the Chinese branded a 'cheap trick' to upset him.
The dig was a reference to Sun's three-month doping ban for taking a banned stimulant which the Chinese superstar, the 400m and 800m world champion, said was for a heart complaint.
Sun dominated the 400m freestyle event from 2012 until his defeat in Rio and is desperate to re-establish his authority in Budapest.
He has swum the fastest over 400m this year and can stamp his authority from the first day in Sunday's heats and final.
Sparks are expected to further fly with both also registered to swim over 200m, 800m and 1,500m freestyle.
With Michael Phelps, Missy Franklin and Ryan Lochte missing in Budapest, five-time Olympic champion Ledecky will lead the Stars and Stripes' charge having finished with four gold medals at the 2016 Rio Olympics.
Still only 20, Ledecky could scoop six golds in Budapest as she goes in the 200m, 400m, where she could win her first gold on Sunday night, 800m and 1 500m freestyles, plus the 4x100m and 4x200m freestyle relays.
With Franklin absent after shoulder surgery, Ledecky could break her US team-mate's record of six gold medals set at the 2013 world championships.
Expect victories by big margins from the Stanford University student.
When she won the 1500m freestyle title in Kazan two years ago, Ledecky's winning margin was 15 seconds ahead of New Zealand's Lauren Boyle, who swam an Oceania record.
The 22-year-old has won every 100m breaststroke race he has entered since the 2014 Commonwealth Games.
Britain's gold-medal machine holds the world records over both 50m and 100m, the latter of which he set in winning the 2016 Olympic final in Rio, and is threatening to go even faster in Budapest.
Peaty will again be locking horns with South Africa's Cameron van der Burgh as he defends his 50 and 100m titles.
After his Rio success, Peaty had a lion tattooed on his left shoulder and you can expect him to roar out of the blocks in Sunday's 100m heats.
With arch-rival Michael Phelps now back in retirement, South Africa's Le Clos has a point to prove and is expected to be a force over 100 and 200m butterfly in Budapest, as well as the 200m freestyle.
Le Clos failed to defend his Olympic title when he finished fourth in 200m fly final in Rio.
He also finished joint second - alongside Phelps and Hungary's Laszlo Cseh - in the 100m fly after Singapore's Joseph Schooling pulled off a shock win.
Le Clos will be defending his 100m world title and will battle Cseh, who beat him in the 200m fly at the 2015 world champs in Kazan, over the longer distance.
Hungary's 'Iron Lady' will be on home turf in Budapest's Duna Arena on the banks of the Danube.
The 28-year-old has an iron grip on the 200m and 400m individual medley titles as the Olympic and world champions holds the record in both events.
Hosszu has entered six individual events, including the 100m backstroke in which she is the Olympic champion, an exhausting schedule which will test her nickname, especially if she is added to Hungary's relay squads.
Watch out for Hosszu's performance in the 400m IM after she won Olympic gold in Rio by smashing a further two seconds off Ye Shiwen's world record, which sent shockwaves through the 2012 London games.