Rey started out as a wrestler at the age of 16 in Mexico under the name 'Colibri'. This was after only two years of training by his uncle, Rey Mysterio. After wrestling independent shows in California, and after his success south of the border, his uncle persuaded him to change his ring name to 'Rey Mysterio Jr'.

They began tagging together drawing much fan support and after Rey Mysterio jumped ship to the AAA, Jr. went along with him.

Many stories have been told that Rey used to do his Math Homework in the locker room before matches, but he soon left High School in the 11th grade to become a full-time wrestler.

He soon found his ideal opponent: Juventud Guerrera. The two had many memorable matches, and both Rey Mysterio and Fuerza Guerrera(Juvi's father) became involved in the fued. He also fought Psychosis to many classic matches. They claim to have wrestled eachother over 150 times.

Jr soon found major fan support abroad as he wrestled briefly in Japan and then had a short stint with ECW. Then WCW gave him a call.

The US fans were amazed at Rey's high flying talent and good mat skills. The match which is thought to establish him as a star was his win over Psychosis at Bash at the Beach 1996. Mysterio reversed a Splash Mountain into a hurricanrana of the top-rope to seal the win in the opening bout of the card. This was the same night in which the nWo formed.

He went on to have famous clashes with Jushin 'Thunder' Liger and Eddy Guerrero, the last of which was when Guerrero pinned Rey at Halloween Havoc '98. As a result of this, Jr was forced to join the LWO. At first he was a reluctant member of the group, not happy with their evil ways and cheating during matches. But when the rest of the faction took the money from Ric Flair to stop the madness, Rey suprisingly kept on his shirt.

When the nWo Wolfpac reformed, they went on a mission to destroy any other organisations. With Rey the sole member left, he refused to take off the LWO shirt, and Konnan defended him for it. As a result. 'K-Dogg' was booted from the Wolfpac.

This led to a tag-team match against Kevin Nash and Lex Luger at Superbrawl '99, where the stipulation was Rey's mask against Miss Elizabeth's hair. After interference, Rey and Konnan went down to a loss and Mysterio was forced to unmask. This perhaps was blessing in disguise, as it only earned him more popularity.

Rey wanted revenge on Nash, and he pinned him cleanly in the middle of the ring on NITRO the day after Superbrawl. He then went on a winning streak, defeating Super-Heavyweights Scott Norton and Bam Bam Bigelow in consecutive weeks. When Nash and Rey met again at Uncensored, 'The Giant Killer' was on the verge of victory, until Lex Luger interfered and Nash got the win.

After this, he started tagging with Kidman, and they won the Tag Team Championship after fueding with Dean Malenko/Chris Benoit and Raven/Perry Saturn. Rey then went on to capture the World Cruiserweight Title for a record fifth time.

Rey then joined the ultimately unsuccessful No Limit Soldiers group with Konnan, but when it collapsed, he formed The Filthy Animals along with Konnan, Kidman and long-time enemy Eddy Guerrero.

After fueding with The Revolution, he was sidelined with a knee injury. After returning when Vince Russo and Eric Bischoff came to power in WCW, he had a brief stay in the New Blood faction with the rest of the Animals, and soon it was revealed that Tygress was his girlfriend.

The Filthy Animals soon turned face again, and have more popularity than ever.