Yes, Rey Mysterio has been a heel.
Rey Mysterio became a heel for the first and only time in his career after he formed a stable with Eddie Guerrero and Billy Kidman known as the Filthy Animals.
The American professional wrestler Óscar Gutiérrez is currently signed to WWE, where he performs on the SmackDown brand under the ring name Rey Mysterio.
Born on December 11, 1974, in Chula Vista, California. Mysterio commenced his wrestling career at an early age in Mexico where was trained by his uncle Rey Misterio Sr. who is a Mexican retired professional wrestler and trainer.
After passing through Asistencia Asesoría y Administración, Extreme Championship Wrestling, World Championship Wrestling, and Consejo Mundial de Lucha Libre, Rey joined World Wrestling Entertainment in 2002.
In his WWE career, Rey has attained many accolades including World Heavyweight Champion (2005–2007), Intercontinental Champion (2009–2010), World championship reigns (2010–2011), and others.
On Saturday, April 1, 2023, Rey Mysterio faced his son Dominik on WrestleMania 39 which Rey won the match.