The katra, or living spirit, was the essence of the Vulcan mind and could be transferred to another person or preserved in katric arks before death. Described as a Vulcan's eternal life force, it was likened to their soul. (ENT: "Awakening"; DIS: "Lethe"; Star Trek III: The Search for Spock; VOY: "Innocence")
During the mid-22nd century, existence of the katra was controversial; many Vulcans thought it was nothing more than a myth, but a small group of Vulcans named the Syrrannites believed in it. It was also alleged that ancient Vulcans used katric arks to preserve katras. However, a set of katric arks found at the P'Jem monastery some centuries before the 22nd century, upon analysis, yielded no evidence to indicate the presence of a katra. (ENT: "The Forge", "Awakening")
Syrrannite assertions about katras proved to be correct when in 2154, the katra of Surak, father of Vulcan philosophy, surfaced and was transferred in front of the Vulcan High Command. Although Surak died in the 4th century, his katra survived to the year 2154. Found and absorbed by a Vulcan called Syrran, it was then briefly held by a Human, Captain Jonathan Archer, before its transferal to a Vulcan priest. The reappearance of Surak's katra was instrumental in the rise of T'Pau's influence and the following reorganization of Vulcan government and society. (ENT: "Awakening", "Kir'Shara")
Workings and possibilities
When a katra was transferred to someone, he or she would benefit from the experiences of the person the katra had come from. Because the katra could resist its transfer, the procedure was not without risk and must be performed according to a specific ritual. Non-Vulcans might experience side effects, like a form of multiple personality disorder. Humans were especially vulnerable because of the severe shock a transfer could give to their nervous system. Restoring a katra to a Vulcan was preferably done by a Vulcan priest with enough experience with katras. (ENT: "The Forge", "Awakening", "Kir'Shara")
Vulcans could initiate a transfer of their katra by placing one of their hands on the head of the recipient and to position their fingers on specific points. Via a mind meld, a Vulcan was able to tell if someone had received a katra.
The katra could be restored after a person had died and his katra had been transferred to someone, if the family of that person wanted to have the katra restored. This ritual was called fal-tor-pan, which literally means "the re-fusion". The ritual was performed very rarely. The last known time was in 2285, when Spock's regenerated body was found on Genesis and returned to Mount Seleya, where his katra was transferred from Doctor McCoy into his own body.
The transfer of someone's katra was not regularly practiced and was only done in special circumstances. When a Human received a katra, the effects of the merge could be counteracted by lexorin, but this was only for a short period of time. The katra must eventually be transferred to someone else. (Star Trek III: The Search for Spock) Around 2369, the existence of the katra was common knowledge within most medical establishments. (citation needed • edit)
The katra had healing power, and could be used to save a wounded person, even a non-Vulcan, through what might be described as a kind of soul graft. As of the mid-23rd century, this procedure was both rare and frowned upon. As a side effect, procedure resulted in an unique kind of connection, more than a mind meld, that might activate even years later and over many light years. In 2256, Paul Stamets experimented with the latter effect, boosting the neural signals of someone who had received such a graft using a neural enhancer in what he called a "synthetic mind meld augment". Stamets was exited about the potential of katras, describing them as an "uncharted superhighway connecting all of consciousness and life". (DIS: "Lethe", "Battle at the Binary Stars")
Notable katra transfers
- In 2154, the katra of Surak was transferred from Syrran into Captain Jonathan Archer, during the aftermath of the bombing of the United Earth Embassy on Vulcan. After four days, the katra was transferred to a Vulcan priest. (ENT: "The Forge", "Awakening", "Kir'Shara")
- Sometime in the 2230s, after a bombing at the Vulcan Learning Center resulted in young Michael Burnham's death, Sarek used his katra to bring her back to life. As a result, Burnham retained part of his katra even years later, and with it, a remote connection Sarek described as "more than a mind meld". In 2256, after Sarek was targeted by Vulcan extremists, Stamets boosted this connection to allow Burnham to revive Sarek so he could send their rescue shuttle a signal. (DIS: "Battle at the Binary Stars", "Lethe")
- In 2268, Spock temporarily had his katra transferred into Nurse Christine Chapel before having it transferred back into his own body. (TOS: "Return to Tomorrow")
- In 2285, Spock transferred his katra to Doctor McCoy, moments before he entered the USS Enterprise's radiation room to give the starship its warp capability back, so the ship could flee the Mutara Nebula before the Genesis Device detonated. Spock died of radiation poisoning, and his body was "buried at sea" using a photon torpedo as a coffin. The torpedo landed on the emerging Genesis planet, though, where his reanimated body was later found and returned to Vulcan. There, on Mount Seleya, the fal-tor-pan ritual was later performed by T'Lar at the request of Sarek, Spock's father, to reunite Spock's katra, carried by Doctor McCoy, with Spock's body. (Star Trek II: The Wrath of Khan; Star Trek III: The Search for Spock)
In the Star Trek: Vanguard series of novels, the Vulcan science officer T'Prynn is a val'reth; she holds the katra of another, her would-be mate Sten, who she challenged for her freedom in the kal-if-fee, against her will, as Sten transferred his katra into her mind as he died and refuses to leave T'Prynn's mind until she submits to his will. It is, however, unclear whether the term "val'reth" refers to T'Prynn having been given the katra without her consent (in which case, Archer and McCoy could also be referred to as "val'reths", considering that neither of them consented to receiving a katra) or whether it refers to the fact that Sten's katra would not allow itself to be removed from T'Prynn's mind.
The novel The Lost Years deals extensively with the concept of katras and katra transfers. The novel speaks of an ancient warrior named Zakal, who died the day before the Romulans left Vulcan during the Time of Awakening, and his katra was stored for over two thousand years. When he was revived in the 23rd century, Zakal's first comment was that the Vulcans apparently hadn't run out of "S-names" for their male population.
The novel Beneath the Raptor's Wing had the katra of Surak surviving in various Vulcan priests after it was transferred from Captain Archer. One priest carrying the katra was killed by a Romulan assassin and the katra was lost, with Archer feeling this loss due to the time he spent carrying the katra despite being several light years away.