The Ancients are a fictional alien species on the science fiction television series Farscape. They are technologically and physically advanced and have the ability and knowledge to harness wormhole-based technology.
The Ancients originally existed in another realm, one that is vastly different from our own. This plane of existence was bridged to ours by wormholes. When they became aware of the various species in our realm, and many of those species' aggressive tendencies, they modified several members of their own species, allowing them to live and exist in our universe. These individuals became the Ancients and they were tasked to catalogue, report, and influence the activities of the species in our universe.
After many years in our realm, however, the planet where the Ancients lived began to die. They started a search for a suitable location whose dominant species would welcome them and where the Ancients' hive could live and replenish. The Ancients only had enough power to transport their entire race one last time and because of their unique nature, they could only live on a small number of worlds. Discovering that Earth was one of these worlds, the Ancients created an elaborate simulation using the memories of the human John Crichton. Creating what appeared to be a wormhole leading to Earth, the Ancients lured John into the simulation. There, Crichton's memories and expectations played out a scenario that allowed the Ancients to see how humans would respond to alien arrival. Shortly after Crichton realizes that there is something very wrong about the Earth to which he's returned, an Ancient in the guise of John's father Jack Crichton explains the situation and the reason for the simulation. Having learned that humanity would not welcome an alien species on its planet, they continued their search for a new home. Unknown to Crichton at the time, the Ancients gave him subconscious knowledge of wormhole navigation. Their intention was to give him a potential way home if he proved to be worthy of unlocking that information himself.
The Crichton traveling on Talyn next encounters a member of their race two cycles later, when "Jack" reappears. Initially they believe that Crichton has been careless with the wormhole knowledge given to him, but then they realize that he had shared his wormhole knowledge before meeting the Ancients—to a mechanic named Furlow, on the planet Dam-Ba-Da. Traveling there, they find that Furlow has built a replica of John's Farscape One module and is using it to unlock the secrets of wormholes so she can sell it to the Scarrans. Though "Jack" is killed (by Furlow) in the encounter, he does unlock the wormhole knowledge in Crichton's brain, they construct a displacement engine, a device that alters a wormhole to gather a large amount of plasma from a nearby star to be used as a weapon. They then use it to destroy a Scarran Dreadnought in order to keep wormhole technology out of their hands.
One cycle later, the other Crichton encounters a being who belongs to the Ancients' species, though he was not modified to exist in our realm. This individual, nicknamed "Einstein" by Crichton, is curious about why the Ancients decided to give Crichton wormhole knowledge. He explains that his species has investigated why the Ancients disappeared from our universe. In doing so, they were alarmed to discover Crichton's extensive knowledge of wormholes and the many aggressive species hunting him as a result. Though Einstein originally intends to end the threat by killing Crichton, he eventually lets John go, albeit after warning him about the many dangers of careless wormhole travel.
Months later, Crichton takes Scarran Emperor Staleek to see Einstein to confirm for him that Crichton cannot make a wormhole weapon. Einstein would later give Crichton the knowledge needed to construct such a weapon. After Crichton uses the weapon to intimidate the Scarrans and Sebaceans into declaring a truce and ceasing their search for wormhole weapons, Einstein removes the knowledge of how to build the weapon from Crichton's brain. With the knowledge gone, Einstein's original mission is complete and he presumably returns to his own realm.
The Ancients have technology and knowledge that greatly exceeds anything seen in our galaxy. They have the ability to understand and use wormhole travel and navigation. Their wormhole-based technology includes at least two wormhole weapons. In their own realm, time is subject to an Ancient's will. In our own realm, they also have the ability to create extremely realistic simulations based on a subjects' memories. These are not virtual reality, but actual duplications down to identical-seeming people and materials. These simulations are limited to only what is in the subject's memory, so when Crichton realized that everyone in "Australia" was someone he had also known in his own past in America, the Ancients' duplicity was revealed.