Last time around Phelps captured the attention of the nation, winning an Olympic-record eight gold medals in a single Games.
This time around, the Baltimore native is looking to set the all-time record for total medals. He's only two behind Soviet Union gymnast Larisa Latynina's count of 18, and could easily surpass that total this year.
However, this time Phelps will be forced to share the spotlight with a myriad of other talented Americans.
Here are a few swimmers who could vault into the U.S. mainstream in London as they go for gold.
Missy Franklin is the female version of Phelps.
She is competing in seven events in London, and is so talented that she has a great chance to medal in all of them.
If that's not impressive enough, she is only 17 and hasn't even finished high school yet.
Despite her youth, Franklin is already a powerhouse on the international stage. At the 2011 World Championships Franklin earned five medals, including three golds.
She stands as the brightest-shining female star entering the games, and thankfully for audiences, she has the personality to match.
She’s outgoing in her interviews, always has a huge smile on her face and is even known for her dancing prowess.
Franklin has the talent and the charm to enthrall audiences in a few weeks, and by the end of the games it could be her name and not Phelps' that captures headlines.
Franklin isn't the only potential teen phenom at these games: 19-year-old Elizabeth Beisel could also make a major splash.
Beisel is competing in two individual events and will have an opportunity to win even more medals in relays.
Beisel qualified for the games by winning the 400m IM, an event she won at last year's World Championships, and by finishing second in the 200m backstroke.
Though she is young, Beisel has already dealt with the pressure that comes with the Olympics. In 2008 as a 15-year-old, she narrowly missed medaling in a pair of events.
However, now she is more experienced. In London she should easily earn a medal, and could even capture a pair of elusive golds.
Phelps may be the world's most famous swimmer, but, as of now, Ryan Lochte is the best.
After Phelps dominated in 2008 he took a step back as far as training and work ethic goes (h/t The Press-Enterprise), to take a break from swimming. In that time Lochte only improved, and over the last four years he has transformed into the best swimmer on the planet.
In the 2011 World Championships Lochte dominated, winning five gold medals. This includes a head-to-head victory over Phelps in the 200m IM.
At the trials, Lochte qualified for four individual events, and will add to that total with some additional relays.
Like Phelps, Lochte will likely compete in seven events, as he looks to add to his lone individual Olympic gold.
Lochte will go up against Phelps in both the 200m IM and the 400m IM. It will be the results of these events that will determine who is the best swimmer on the planet.
If Lochte comes away victorious in both of these races, Americans will have a new swimming sensation on their lips.