Einstein begins to test Crichton by showing him various unrealized realities, pulling him from each before the human became a permanent part of any of them. These experiments left Einstein weakened, though he realized he had been mistaken: though Crichton was dangerous because of his wormhole knowledge, removing that knowledge from him was "impossible, impractical, and possibly imprudent."
During the Scarran/Peacekeeper War, Einstein encountered Crichton again -- this time along with Emperor Staleek. Einstein confirmed for the Scarran emperor that Crichton could not create a wormhole weapon.
Later, upon realizing that creating a wormhole weapon would be able to end the war, Crichton returned to Einstein and demanded that the Ancient unlock the knowledge of such technology. Einstein was eventually convinced to do so -- however, when Crichton was unable to stop his wormhole weapon after the war was ended, Einstein appeared and both stopped the expansion of the black hole and removed wormhole knowledge from Crichton's brain.
"Einstein" is a character from Farscape.