Ian Lowell Crocker (born August 31, 1982) is an American former competition swimmer, five-time Olympic medalist, and former world record-holder.

At the 2000 Summer Olympics in Sydney, Crocker was a member of the gold medal-winning 4x100-meter medley relay team[4] and barely missed winning a bronze in the 100-meter butterfly.

In his first event, the 50-meter butterfly, Crocker won a silver medal finishing behind Australian Matt Welsh, who set the world record.

[14] Of the three medals he won at the 2004 Olympics, he is best remembered for his silver, as teammate Michael Phelps overtook him at the very end of the 100-meter butterfly to win the race by 0.04 seconds.

Traditionally, the Olympian who places highest in an individual event will be automatically given the corresponding leg of the 4×100-meter medley relay for the finals swim.

This gave Phelps an automatic entry into finals for the medley relay but he deferred that spot to the world record-holder and swam the butterfly leg in preliminary heats instead.

In his first event, the 50 m butterfly, Crocker won a silver medal finishing behind South African Roland Schoeman, who set the world record.

Many felt Crocker's career was on a slide due to a poor showing in the Olympic trials and having not broken the 51-second barrier in over 12 months.

In the finals, he finished fourth behind teammate Phelps, Milorad Čavić, and Lauterstein, beating Kenyan swimmer Jason Dunford.