The substance with the highest known energy per unit volume in the universe. Raw quintessence material is transported here from throughout the galaxy and refined into standardized Galra fuel requirements.—Galra Sentry, in "Collection and Extraction"
Quintessence is a substance with the highest known energy per unit volume in the universe. Raw quintessence is capable of being extracted from planets and refined into a standardized fuel for Galra technology. It is said to be life itself and a self-generating power source. Raw quintessence appears to be yellow or white in color. Quintessence refined by Druids for the Galra Empire appears violet.
Quintessence is seen in various forms:
- Yellow: Raw quintessence. The Druids take this and convert it into purple quintessence, as seen in Season 1 Episode 10 - 'Collection and Extraction'.
- Purple: Standard fuel for Galra technology. When injected into living beings such as Haggar's Robeasts, the Beta Traz Warden, and later on Zarkon through his armored suit, it causes massive increase in a subject's size, strength, and speed, at the potential cost of their sanity.
- White-Blue: Concentrated quintessence. Lotor uses this to try and travel through the inter-reality gate that he had constructed over the dimensional rift left by the landing of the trans-reality comet. It is implied to be very powerful, as it overloads Kolivan's monitor in season 4 episode 1 'Code of Honor'. It is later discovered in season 6 episode 4 - 'The Colony' that some of this form of quintessence is harvested by Lotor from living Alteans.
It is heavily implied that Zarkon's unnaturally long lifespan as well as his immense physical strength is due to regular infusions of refined quintessence. His change of personality from honorable Paladin to monstrous dictator is also due to the influence of quintessence, which exacerbates an individual's worst traits and can drive them to insanity.
Throughout the first season of Voltron: Legendary Defender, we see multiple references to the substance. The most common example is Zarkon's ability to levitate between numerous spires that blast the energy at him, and it is hinted at as an explanation for his longevity.
The Galra Empire takes over planets in order to harvest quintessence, and they find that the crystals that Balmera naturally produce can contain quintessence. The Galra use mining shafts to dig deep into the Balmera and harvest the crystals. Unfortunately, this leaves no room for the Balmera to gain something in return, and thus, the only seen Balmera, X-95-Vox, is severely damaged when the Galra mine it.
Later in the first season, Haggar creates a massive device called the Komar Experiment that harvests all possible quintessence from a planet, leaving it completely barren of any life. Zarkon remarks that this will allow them to quickly gain massive amounts of quintessence, which would normally have taken years with mining and colonization.
Being a substance described as essentially life itself, the key aspect of quintessence seems to be its ability to heal lifeforms and enable longevity. The transfer of quintessence from Sacred Alteans to Balmera planets after power Crystals are harvested is a feat Allura is able to accomplish with her abilities to absorb and channel quintessence A simple touch or her presence on the planet surface is enough to restore the area she is contact with.
The healing property of the substance extends to small amounts on smaller lifeforms: After Keith is wounded by a Druid and knocked into a canister of raw quintessence, breaking it and spilling it over himself, the quintessence spilled on him heals is wounds shortly after the fact.
The opposite effect, death of a creature or planet, holds true when quintessence is extracted, as seen in Haggar's Komar Experiment, where a planet becomes completely barren when its entire quintessence is sapped from it in a matter of moments. Overexposure to quintessence is damaging to health and potentially fatal.
Longevity & Alteration
Quintessence is shown to enhance the abilities and alter the body of lifeforms it is absorbed by; this is discovered when Honerva used quintessence to heal Kova allowing the alien cat to live for 28 deca-phoebs, or years, and continue living for another 10,000 years. This aspect is what enables Zarkon to grow in power and continue living for 10,000 years himself, after he and Honerva seemingly "die" and resurrect. The mystical substance, coupled with mysterious darkness from an Alternate Reality, reawakens him and his wife from "death" and alters both of their minds. Quintessence is used by Haggar to create Robeasts, able to turn a simple lizard into the terrifying Drazil, or make a Robeast out of measly Galra commanders.
Lions and Power Source
Allura describes the quintessence of Paladins as being mirrored in their respective Voltron Lions, as a mystical bond that cannot be forced nor explained by science. This is because the ore of the Lions is quintessence-infused trans-reality material. A single drop of quintessence is able to power a simple machine for an entire year with no loss in performance. This principle is what powers the Lions and grants them a seemingly endless supply of energy.
- The idea of Zarkon extending his lifespan with substances was touched upon in the original Voltron series, where Zarkon briefly mentioned using the flowers from the planet Lyra to extend his already long life. 
- Per Wiktionary: Etymology: Middle English, from Middle French, from Medieval Latin quinta essentia "fifth essence".
- Noun: quintessence (countable and uncountable, plural quintessences)
- A thing that is the most perfect example of its type; the most perfect embodiment of something; epitome, prototype.
- A pure substance.
- The essence of a thing in its purest and most concentrated form.
- (alchemy) The fifth alchemical element, or essence, after earth, air, fire, and water.
- (physics) A hypothetical form of dark energy postulated to explain observations of an accelerating universe.
- Infusion with a living being seems to cause emaciation and gradual insanity of the user, as Honerva and Kova seem drastically lose weight and suffer radical changes in personality. The mental corruption can also possibly passed to the victim's child, as seen in case of Lotor.
- Though not confirmed, Rift creatures may comprised of pure quintessence.
- Lauren Montgomery compares quintessence to that of the Star Wars "Force", that it exists to some degree in everything and explains the explainable. Dos Santos claims it is what the universe is powered on.
- Montgomery and Joaquim Dos Santos elaborate that quintessence, like medicine, is good in small doses, but too much can be fatal. The substance is not inherently good nor evil, but can grab hold of the negative aspects of a person and greatly accentuate them, leading to corruption.