The professional wrestling matches at SummerSlam featured professional wrestlers performing as characters in scripted events pre-determined by the hosting promotion, World Wrestling Entertainment (WWE). Storylines between the characters were produced on WWE's weekly television shows Raw and SmackDown! with the Raw and SmackDown! brands—storyline divisions in which WWE assigned its independent contractors to different programs.
World Heavyweight Champion Triple H
In the first main event of SummerSlam wrestlers from the Raw brand competed in an Elimination Chamber match, in which the ring is surrounded by a steel structure of chain and girders. The match was contested for the World Heavyweight Championship, in which Triple H defended the title against Chris Jericho, Goldberg, Kevin Nash, Randy Orton, and Shawn Michaels. The buildup to the match began on July 22, 2003, when during the SummerSlam press conference, the authority figure Eric Bischoff, announced that Triple H would defend the championship against Goldberg in a standard wrestling match at the event. On August 4, 2003 during a television episode of Raw, Bischoff changed the stipulations of the match to No disqualification regulations. Later during the episode, another authority figure, Steve Austin, altered Bischoff's announcement, stating that the championship would be contested in an Elimination Chamber match, with Triple H defending his title against Goldberg, Chris Jericho, Kevin Nash, Randy Orton, and Shawn Michaels. Six days before SummerSlam, during an episode of Raw on August 18, 2003, the rivalry among the six competitors intensified during a promotional interview segment, in which each participant in the Elimination Chamber discussed the match and taunted the other wrestlers. During the show's main event, in which Orton wrestled Goldberg, Nash interfered in the match and attacked Goldberg. Michaels then came down to the ring, but as he was about to hit Triple H with the World Heavyweight Championship belt, Jericho ran into the ring and hit Michaels with a chair.
Kurt Angle, the WWE Champion heading into SummerSlam
The second main event resulted from events on SmackDown!, WWE's other main television program. In the match, Kurt Angle defended his WWE Championship against Brock Lesnar. The build-up to the match began on July 31, 2003 on an episode of SmackDown!. During an interview promotion in the ring, Lesnar challenged Angle to a rematch of their bout at Vengeance, WWE's previous pay-per-view event. The WWE Chairman, Vince McMahon, decided that Lesnar would have to earn his rematch by competing in a steel cage match against McMahon himself, and would take place on SmackDown! the following week, with Angle officiating as a special guest referee. The Steel Cage match resulted in neither wrestler winning the match, after McMahon and Lesnar attacked Angle. On August 14, 2003 during an episode of SmackDown!, McMahon announced that Angle would defend the championship against Lesnar at SummerSlam.
In a preliminary match involving wrestlers from the Raw brand, Rob Van Dam wrestled Kane under No disqualification regulations. The events leading up to this match began on the June 23, 2003 edition of Raw, when Kane took his mask off and exposed his face in front of RVD and the crowd after he lost to Triple H during a World Heavyweight Championship match. Then, on July 7, 2003, when Kane attacked Van Dam backstage during an episode of Raw. The following week on an episode of Raw, Eric Bischoff granted Van Dam a standard match against Kane, which took place the following week on Raw and ended in neither wrestler winning the match. On August 4, 2003, Shane McMahon, the son of Mr. McMahon, scheduled a No Disqualification match between the two wrestlers for SummerSlam.
In another preliminary match, wrestlers from the SmackDown! brand competed in a match between four wrestlers for the WWE United States Championship: Eddie Guerrero defended the title against Chris Benoit, Rhyno, and Tajiri. The buildup to the match began with two different rivalries, one between Guerrero and Tajiri, and the other between Benoit and Rhyno. On August 7, 2003 during an episode of SmackDown!, Guerrero and Benoit wrestled in a standard match. However, during the match, Rhyno and Tajiri interfered, resulting in neither wrestler winning the match. Sgt. Slaughter, a WWE official, scheduled a tag team match between the team of Guerrero and Benoit and the team of Rhyno and Tajiri, which Guerrero and Benoit won. The following week on an episode of SmackDown!, a SummerSlam advertisement announced that Guerrero would defend the WWE United States Championship against Benoit, Rhyno, and Tajiri.