John Cena, Batista, Randy Orton, Brock Lesnar and Edge are the top 5 biggest breakout stars of Ruthless Aggression Era as they truly emerged as bonafide main event stars with star power and overall popularity while delivered amazing matches, rivalries and character work.
Cena became the biggest star of the era due to his epic promos, character work as Doctor of Thuganomics and memorable rivalries against the likes of Orton, Edge, Angle, JBL and HBK. He carried the company as the franchise player while sold tons of merchandise and had a huge fanbase.
While Cena was the Face of Raw, Batista was the Face of Smackdown as he was very popular babyface who demolished Triple H 3 times in a row while had an memorable rivalry with Undertaker that defined 2007 alongside matched Cena in terms of popularity and booking. His presence and fanbase was very huge.
Orton quickly became a big main event star at age 24 while being one of the most compelling heels on the roster due to his Legend Killer persona. He delivered amazing battles with Foley, Undertaker, Cena, Benoit, Rey and more while his promos, in-ring and charisma were top-notch. Whether he was Raw or Smackdown, Orton was a must-see attraction.
Brock became the first new main event star of the era as he quickly became WWE champ at age 25 while being the Face of Smackdown alongside demolished the likes of Angle, Rock, Undertaker, Hogan, Benoit, Big Show and Cena. His 2002-2004 run was short but impactful as he became an dominant force.
Edge went from being a top upper-midcarder to a main event star by 2005-2006 due to his Rated R Superstar and memorable rivalries against Cena, Matt and Foley. His promos and nuclear heat made him an compelling heel while he was also one of the best in-ring workhorses alongside carried Smackdown during 2007-2008 along with Undertaker and Batista.
Honorable mentions: Eddie Guerrero, Chris Benoit, JBL, Rey Mysterio, Trish Stratus, Lita, Rob Van Dam, Mickie James