Dr. Eisenstein, known in Japan as Dr. Albert Zweinstein, is a ten time Nobel award-winning German medical doctor with an IQ of 173 that specializes in Duel physics.
Eisenstein arrives at Duel Academy under Prince Ojin's request and is sent by Sartorius to eliminate Jaden and retrieve his key to the mind control satellite although his underestimation of the young duelist's tactics results in his failure. Bastion idolizes him for his unified theory of the world constituting a "beautiful space" and calls him a "god".
He returns during the third year (Episode 126) to communicate with those trapped in the other world, informing them that the key to their escape is to send Jesse's "Rainbow Dragon" card through a wormhole to link both dimensions.
His last name, in both the English and Japanese versions of the anime, is a pun on the name of Albert Einstein and as such is based on him in voice, therefore he speaks with a German accent.
Eisenstein plays a Relativity Deck. Being a Duel physicist, Eisenstein has researched extensively the interactions between Monster, Spell, and Trap Cards, coming to the conclusion that science overtakes any sort of "miracle" or "luck". He occasionally quotes Albert Einstein's assertion that "God does not roll dice", meaning that the universe is not ruled by chance. As such, his Deck exploits statistics and probability, yet in doing so, ignores alternative methods of achieving identical results as with Jaden's use of Contact Fusion. References to Einstein's interests are made throughout his deck, including mentions of "Pierre-Simon Laplace" and Schrödinger's cat.