Michael Phelps is already the greatest Olympian of all time, but he is not yet finished writing his legacy.

Starting tonight, he has three more opportunities left to win gold and break Mark Spitz’s record of seven golds in one Olympics. His final three races include the 100-meter butterfly, the 200-meter individual medley, and the 4×100-meter medley relay.

Phelps’s 200 IM final, which airs live tonight, is one of the hardest events in the sport of swimming: Two-hundred-meter races are typically the least favorite of swimmers, because they are a hybrid of sprint and distance, requiring the swimmer to judge how much energy to conserve and use throughout the race. The 200 IM involves 50 meters of each stroke, using the butterfly, backstroke, breaststroke, and freestyle, in that order.

Phelps won gold in this event in Athens, clocking in at one minute and 57.14 seconds, and he took gold at the 2007 World Championships, earning a world record time of 1:54.98.

Expect a showdown between Phelps and fellow American Ryan Lochte, who’s considered a medley specialist. Even though Phelps holds the record in this event, he only earned a 1:58.65 in the Olympic preliminaries, while Lochte swam at 1:58.15. Lochte has also won a silver medal in the event, during the 2004 Athens games. He’s recovered from a stomach virus that he’s been wrestling with since arriving in Beijing, and should be ready to fully compete. Other top contenders in the 200 IM include Hungary’s Laszlo Cseh, who won his heat yesterday in 1:58.29. Cseh is a solid swimmer, having already won silver in the 400 IM on Sunday.

Tomorrow’s final swim in the 100 fly is a must-watch race: Phelps will be racing against fellow American Ian Crocker, his longtime rival in this event. Crocker, the 25-year-old from Portland, Maine, is a butterfly specialist, but Phelps is a master butterflier: When he gets into a groove, he exhibits a wingspan of about 6-feet-7-inches.

It’s been a literal tug of war between Phelps and Crocker, historically, in this event. At the trials in Omaha, Neb., Phelps took first in the 100 fly at 50.89 seconds, with Crocker clocking in at 51.62. He also took gold in the event at Athens, outswimming Crocker at 51.25. A year later, though, at the 2005 World Championships, Crocker fought back by claiming the world record in the event with a time of 50.40.

Since then, Phelps has out-touched Crocker in the 100 fly, including winning gold at the 2007 World Championships. But Crocker still holds the fastest time, and he took gold in the event at the 2002 and 2006 Pan-Pacific Championships. Crocker, an alumnus of the University of Texas’s elite Longhorn Aquatics swim team, trains under Eddie Reese, who is also the coach of Aaron Peirsol and Brendan Hansen. While Crocker is promising, he needs to be mentally sharp under Phelps’s spotlight: Crocker was rattled after disqualifying at the 400 medley relay at the U.S. Championships in 2007.

In Beijing, Crocker and Phelps are expected to medal in the 100 fly, but there are several international contenders who could outswim them. France’s Fred Bousquet holds 51.50 in the race, earned at the French Olympic trials in April (the third-fastest time in the world this year), and Venezuela’s Albert Subirats was the bronze medalist at the 2007 World Championships, with a time of 51.82. In the sport, the 100 fly is considered one of the most physically taxing events, because the butterfly is one of the hardest strokes, and the race is an all-out sprint.

Saturday night’s final of the 4×100 relay will most likely be the most watched of all races, as this will determine if Phelps can clinch the gold medal record. It also happens to be one of the most exciting races to watch in swimming: Each swimmer takes 100m of four strokes, leading with the backstroke, followed by the breaststroke, butterfly, and freestyle strokes. In the 2004 games in Athens, the American squad included Peirsol, Hansen, Crocker, and Jason Lezak. An event that America traditionally dominates (the men’s team has never earned less than gold in this race), look for Peirsol (backstroke) and Hansen (breaststroke) to head the first two legs of the race, with Phelps at butterfly, and possibly Lezak swimming the anchor leg of freestyle. The final team roster will be determined later this weekend.

While Phelps is existing quietly in Beijing, preparing for races and doing little else, his celebrity is making its impact felt throughout the American press. In the shadows of his enormous fame are two individuals who have helped him thrive in and out of the lane — his mother, Debbie, and his coach, Bob Bowman. Debbie Phelps raised Michael and his sisters on her own after her divorce. While Phelps is close with his mother and sisters, he is not close with his father.

Phelps’s complex relationship with his longtime coach is legendary, beginning when he was only 11 years old. The two were matched in 1997, when Phelps was assigned to Bowman’s group at the North Baltimore Aquatic Club.

Bowman has compared the relationship to that of an old married couple at times. “When we started, it was just Michael and me. I was his coach, his guardian, his friend,” Bowman said in an interview with USA Swimming in 2007. “We’ve had a decade together, and there’s been some incredible things we’ve been through. We’ve been through a lot of different things that most families and married couples haven’t even been through.”

The two know each other so well that Bowman said they often communicate without speaking. “We talk by signals at times,” Bowman laughed. “We can just tell what each other thinks.”

Their relationship was played out in the 2005 documentary “Unfiltered,” where Bowman is seen snapping at his pupil, who responds by taking off his swim cap and leaving the pool — but all is forgotten later that day.

The coach and swimmer are already looking to the 2012 Olympic Games in London. In the meantime, the world holds its breath to see whether Phelps will take home eight gold medals.

Ms. Wu is a contributing writer for Swimmer magazine.