WrestleMania 21 was the twenty-first annual WrestleMania professional wrestling pay-per-view (PPV) event produced by World Wrestling Entertainment (WWE). It took place on April 3, 2005 at the Staples Center in Los Angeles, California.

The event was a joint-promotion pay-per-view, featuring performers from the Raw and SmackDown brands. The main match on the Raw brand was Triple H versus Batista for the World Heavyweight Championship, which Batista won by pinfall after executing a Batista Bomb. The predominant match on the SmackDown brand was John "Bradshaw" Layfield versus John Cena for the WWE Championship, which Cena won by pinfall after performing an FU. Another primary match was an interpromotional match between The Undertaker versus Randy Orton, which Undertaker won by pinfall after performing a Tombstone Piledriver. The featured matches on the undercard were Kurt Angle versus Shawn Michaels and a Money in the Bank ladder match. The event also featured the return of Stone Cold Steve Austin who started his part time appearances with WWE at this event.

Steve Austin (born Steven James Anderson, later Steven James Williams; December 18, 1964), better known by his ring name "Stone Cold" Steve Austin, is an American film and television actor, producer, and retired professional wrestler. Austin wrestled for several well-known wrestling promotions such as World Championship Wrestling (WCW), Extreme Championship Wrestling (ECW) and most famously, the World Wrestling Federation (WWF). Described by WWE (formerly the WWF) chairman Vince McMahon as the most profitable wrestler in the company's history, he gained significant mainstream popularity in the WWF during the mid-to-late 1990s as "Stone Cold" Steve Austin, a disrespectful, beer-drinking antihero who routinely defied McMahon, his boss. This defiance was often shown by Austin flipping off McMahon and incapacitating him with the Stone Cold Stunner, his finishing move. McMahon inducted Austin into the WWE Hall of Fame in 2009.

Austin held twenty championships throughout his professional wrestling career, and is a six-time WWF Champion as well as the fifth Triple Crown Champion. He was also the winner of the 1996 King of the Ring tournament, as well as the 1997, 1998 and 2001 Royal Rumbles. He was forced to retire from in ring competition in early 2003 due to a series of knee and neck injuries sustained throughout his career. Throughout the rest of 2003 and 2004, he was featured as the Co-General Manager and "Sheriff" of Raw. Since 2005, he has continued to make occasional appearances. In 2011, Steve Austin returned to WWE to host the reality series Tough Enough.

Rey Gutierrez Mysterio Jr. (born December 11, 1974) is a Mexican American professional wrestler in World Wrestling Entertainment currently wrestling on the RAW Brand. In WWE, Gutierrez was trained by his uncle Rey Misterio, Sr. and wrestled early on in Mexico where he learned the Lucha Libre high flying style that has been his trademark.

Gutierrez originally worked for Asistencia Asesoría y Administración (AAA) in Mexico, from 1992 to 1995. He wrestled in Extreme Championship Wrestling (ECW) from 1995 to 1996 and World Championship Wrestling (WCW) from 1996 to 2001, as Rey Misterio, Jr./Rey Mysterio, Jr. but dropped the "Junior" from his name when he began working for WWE in 2002.

Mysterio is known for having a high flying style, which helped kick-start the cruiserweight wrestling revolution in the United States in the late 1990s during his time in WCW. In WCW he won the WCW World Tag Team Championship three times, and the WCW Cruiserweight Tag Team Championship once with Billy Kidman as part of the Filthy Animals. In WWE, Mysterio is a three time world champion having held the World Heavyweight Championship twice, the WWE Championship once and is currently listed as the lightest world champion in WWE history. He has also held the WWE Tag Team Championship a record-tying four times, and the WWE Intercontinental Championship twice. He also held the WCW/WWE Cruiserweight Championship a record eight times (five times in WCW, three in WWE). All totaled, he has won 21 titles between WWE and WCW. Mysterio was the 21st person to win the WWE Triple Crown Championship, and was the winner of the 2006 Royal Rumble.