From questions about Phelps' struggles with attention deficit disorder to Lewis' take on the racial makeup of most of the world's top sprinters, the pair also spoke about their own achievements.
"I'm never satisfied," Phelps said of his desire to be the best swimmer in the world. "I always want to do better than I did last time."
When it comes to the Olympics, Phelps proved that in Beijing. Four years after winning six gold and two bronze medals at the 2004 Athens Games, the American swept all eight of his events at the Water Cube to become the most successful Olympian.
That feat was certainly not lost on Lewis, a former world-record holder in the 100 meters who collected 10 Olympic medals in his career, including nine gold.
"Before this year, I used to always brag about winning nine gold medals. You taught me about changing rules," Lewis said as he looked over at Phelps. "So now I won the most medals of the last century."
Phelps and Lewis were in the Saudi capital for the Global Competitiveness Forum, appearing alongside Norwegian speedskating great Johann Olav Koss and Special Olympics chairman Timothy Shriver.
Despite the wide range of topics, the one item barely discussed was gender gaps.
The subject is especially sensitive in Saudi Arabia because female participation in sports is highly restricted. The kingdom does not allow female athletes to participate in the Olympics, and female sport leagues and physical education classes in government girls' schools are banned. Female guests cannot even use the gym in most Saudi hotels.
"It's too complicated to talk about in 30 seconds," Lewis told the Associated Press.
Besides the discussion on the panel, Phelps and Lewis also took questions from fans. Khaled al-Sharif, a young Saudi boy who also has attention deficit disorder, asked Phelps what it was like growing up with ADHD and wondered whether it helped him become an Olympic champion.
Phelps told him that he was motivated to excel because he had teachers who said he would never be successful at anything.
"I said to myself, 'I'm going to find something that I can really focus on and show them that if you put your mind to something you really can do it,'" Phelps told al-Sharif. "Swimming ... allowed me to focus."
Discuss this story and others in our talk forumsMost recent sports talk forum topics:More sports talk forums: Orioles | Ravens | Pro Sports | College | Lacrosse | High School | OutdoorsNote: In-story commenting has been temporarily disabled due to technical issues. We are working to correct the issue and will bring back this feature in the future. In the meantime, please use our talk forums to discuss stories.