He was one of mankind's last four survivors in an apocalyptic future, along with Z-one, Aporia and Antinomy. Unlike his fellow survivors, not much of his backstory prior to meeting the other survivors is shown.
His name is derived from the concept of "paradox" in the theory of time. According to it, a paradox is created if the past is altered which then changes the future entirely. This references his mission of changing history by destroying the game of Duel Monsters to prevent his own terrible future from happening, which would have caused catastrophic and drastic changes to the future had he succeeded.
He is the only one of Z-one's comrades to not guard a Planetary Particle as he was defeated before then. Sherry LeBlanc replaces him as the third guard of a Planetary Particle.
An embodiment (different) Paradox is sent from the future after the events of Yu-Gi-Oh! 5D's which has been ruined by the evolution of Duel Monsters. Using his Duel Runner, he traveled back in time in an attempt to rewrite history and create a better future, by eliminating the creator of Duel Monsters, Maximillion Pegasus. Paradox traveled to the New Domino City, during Yusei Fudo's time. He interrupted a Turbo Duel between Yusei, Crow Hogan and Jack Atlas. Yusei has just Summoned "Stardust Dragon", but Paradox absorbed it into a blank card. He showed Yusei the corrupt card, when confronted, before vanishing through time again.
He traveled further back in time to Venice, during Jaden Yuki's time. Once there he started stealing cards from varoius classmates of Jaden, including Jesse Anderson's Rainbow Dragon. Causing massive destruction, Paradox attacked Jaden with "Cyber End Dragon" and "Rainbow Dragon". "Elemental Hero Neos" protected Jaden, so Paradox Summons "Stardust Dragon" to fight off "Neos". However, Yusei who has traveled back in time with help from the Crimson Dragon arrived and saved Jaden. Paradox left and jumped back in time again.
This time, Paradox visited an event where Pegasus is giving cards to young children, in Yugi Muto's time. Paradox used "Cyber End Dragon," "Rainbow Dragon" and "Stardust Dragon" to attack the area, killing many people, including Pegasus and Solomon Muto. Yusei and Jaden arrived in this time and recruit Yugi, who survived Paradox's attack to fight Paradox.
Yusei, Jaden and Yugi traveled back in time to exactly thirty minutes before Pegasus' event and confronted Paradox before he could attack the crowd again. He faces them in a 3-on-1 Duel. Paradox used "Malefic World" and his corrupt "Malefic" counterparts of existing monsters. Yusei, Jaden and Yugi managed to retrieve "Stardust Dragon" from him, and by combining it with their cards, they destroyed Paradox's "Malefic Truth Dragon" and won the Duel, which destroyed Paradox in the process.