Tesseract

"He thought what we think; the Tesseract could be the key to unlimited sustainable energy. That's something the world sorely needs."

- Nick Fury to Steve Rogers

The Tesseract, also called the Cube, was a crystalline cube-shaped containment vessel for the Space Stone, one of the six Infinity Stones that predate the universe and possess unlimited energy. It was used by various ancient civilizations before coming into Asgardian hands, kept inside Odin's Vault. Eventually, it was brought to Earth and left in Tønsberg, where it was guarded by devout Asgardian worshipers.

In 1942, the Tesseract was retrieved by Johann Schmidt, the leader of HYDRA, who used the Tesseract to power enhanced weaponry in order to defeat the Allies during World War II. Following Schmidt's defeat at the hands of Captain America in 1945, the Tesseract fell into Arctic waters, where it was recovered by Howard Stark. After studying the Tesseract, Stark relinquished custody of it to S.H.I.E.L.D., where it remained until it was stolen by Loki who used the Tesseract to open a wormhole and allow the Chitauri to invade New York City. Following the Battle of New York, the Tesseract was acquired by Thor, who brought the Tesseract and Loki back with him to Asgard.

After using the Tesseract to rebuild the Bifrost Bridge, Odin tasked Heimdall, the realm's gatekeeper, with the task of protecting the Tesseract. However, after Loki usurped the throne and disguised himself as Odin, he charged Heimdall with treason, forcing the gatekeeper to flee, while the Tesseract was placed within Odin's vault once more. During the destruction of Asgard, Loki noticed the Tesseract and took it for himself before the vault, along with the planet, were destroyed. Thanos later acquired the Tesseract and crushed it to unveil the Space Stone within and then inserted the stone into his Infinity Gauntlet.

Origins
In the wake of the universe's creation, the six singularities were forged by the Cosmic Entities into the Infinity Stones. The Tesseract was created as a containment vessel for the Space Stone. Within the Tesseract, the Stone was owned and used by various civilizations to achieve their ends.

Ancient Times
"The Tesseract was the jewel of Odin's treasure room."

- Johann Schmidt

The Tesseract came to be kept in the care of the Asgardians during Odin's rule, locked away in Odin's Vault. The Tesseract was brought to Earth by Odin and after being left on the planet it ended up being kept safe in a church in the village of Tønsberg. The Tesseract became the subject of many legends of Norse mythology.

World War II
"The energy we have just collected could power my designs. All my designs. This will change the war." "Doctor Zola, this will change the world."

- Arnim Zola and Johann Schmidt

In March 1942, during World War II, HYDRA forces led by Johann Schmidt invaded Tønsberg where he found the Tesseract in a box hidden behind a sculptured mural of Yggdrasil, the world tree. Schmidt took the Tesseract back to HYDRA Headquarters to be experimented on by Arnim Zola. After experimenting on the Tesseract, Schmidt and Zola were able to harness the object's power to create highly advanced weaponry, fueling Schmidt's plans for world domination.

Zola created batteries that contained the power of the Tesseract, which was then used by him and a handful of HYDRA scientists to power their weaponry. With the power of the Tesseract, Schmidt felt strong enough to turn his back on Adolf Hitler and the. He intended to destroy both the Axis and Allied powers and make himself ruler of the world. In November 1943, Schmidt brought the Tesseract into HYDRA's top secret weapons facility in the Austrian Alps, located halfway between and. During the facility's operation, Allied Prisoners of War were forced to serve in the large-scale assembly of Tesseract based energy weapons including the development of the Valkyrie super-bomber, and a set of nuclear-scale Tesseract energy bombs. When the Allied super soldier Captain America infiltrated the facility to free the four hundred Allied POWs, a large confrontation began. Seeing that his men wouldn't be able to defeat the freed prisoners, Schmidt took the Tesseract and set the base to self-destruct. In March 1945, with his gigantic super bomber, the Valkyrie finally finished, Schmidt was prepared to launch an offensive that would shake the entire planet. With its flying nuclear bombs, Schmidt intended to destroy populated cities across the United States. However, his last base was attacked by Rogers, the Howling Commandos, and a United States Army division led by Chester Phillips and Peggy Carter. Schmidt's men were defeated, but he managed to take the Tesseract and launched the Valkyrie. However, Rogers managed to board the plane and attacked Schmidt, damaging the machine that was using the Tesseract to power the Valkyrie and its flying nuclear bombs. Angered, Schmidt physically handled the Tesseract, only for the object to open a portal, which transported him to Vormir where he became the keeper of Soul Stone. The Tesseract fell burning through the floors, causing it to plunge into the sea below. Sometime later, it was recovered by Howard Stark who was searching for Rogers.

Following the war, a group of former HYDRA scientists managed to escape to South America where they were employed by the government of Peru to make the powerful weapon, using Zola's discoveries of the Tesseract's energy. The scientists were successful, but due to the instability of the Tesseract energy, the weapon ended up stuck in the undiscovered Incan temple.

In the Possession of S.H.I.E.L.D.
"We'd like to have an open discussion regarding the primary objective of S.H.I.E.L.D. as an agency and of you as its director." "You're talking about the Tesseract." "Reigniting the Tesseract. That is correct."

- World Security Council and Nick Fury

After World War II, Howard Stark studied the Tesseract for some time before relinquishing the cube to S.H.I.E.L.D., who possessed the Tesseract-powered HYDRA weapons created by Arnim Zola. At the beginning of the 21st century, Stark's notebook with a drawing of a "hypercube", was found among his research and examined by his son Tony. Tesseract had remained in S.H.I.E.L.D.'s possession and the World Security Council ordered S.H.I.E.L.D. to make one of its primary objectives to reignite the Tesseract and create weapons like Zola had, a project titled Project P.E.G.A.S.U.S..

After an incident in New Mexico during which Thor defeated the Destroyer, humanity finally realized they were not alone in the universe. Erik Selvig was assigned by Fury to research and study the Tesseract with hopes of unlocking its power just as Schmidt had. Later, the Tesseract was moved to the Joint Dark Energy Mission Facility in the Mojave Desert, where Fury also positioned Clint Barton to keep guard over Selvig and the Tesseract.

War for Earth
"I have seen the true power of the Tesseract, and when I wield it-" "Who showed you this power?"

- Loki and Thor In 2012, Loki came into contact with Thanos, powerful warlord and the master of Chitauri. Thanos had already been seeking the Tesseract in order to retrieve the Space Stone, and Loki promised to retrieve it from Earth and give it to Thanos in exchange for his army. Through manipulation of the Tesseract's energy, Thanos teleported Loki to the Joint Dark Energy Mission Facility where he killed several S.H.I.E.L.D. agents and enthralled Erik Selvig, Clint Barton and other agents.

Loki revealed his plans to use the Tesseract to enslave and rule over the human race, and quickly stole the aforementioned object and escaped. The energy from the portal destroyed the entire facility, while Loki took the Tesseract to an undisclosed location.

In response to Loki's threat, S.H.I.E.L.D. decided to re-start the Avengers Initiative and swayed Bruce Banner, Iron Man, and Captain America to their cause. Nick Fury also wanted them to trace the Tesseract as it was emitting small amounts of Gamma Radiation that only Banner and Stark would be able to trace. While Loki was dealing with the Avengers, he ordered Selvig to begin working on a device that could utilize the Tesseract's full power to create a portal that could transport the Chitauri army to Earth. Selvig and Loki later put their plan into effect and opened the portal above Stark Tower in New York City, which unleashed the Chitauri upon the city and an immense battle ensued. Eventually, Black Widow used Loki's Scepter to reverse the effects of the device, shutting down the Tesseract and closing the portal. Following the invasion, Thor returned the Tesseract to Asgard along with Loki. Though World Security Council was very angry at this turn of events, Fury defended his decision to allow Thor to take the Tesseract back to Asgard along with Loki, saying that humanity simply was not at the level where it deserves the Tesseract's power, much to the council's dismay.

Back on Asgard
"Take the Tesseract. Use its power instead of the All-father's to restore what I have destroyed. Let the fires of Bifrost burn once more..."

- Thor to Heimdall After his return to Asgard, Thor gave the Tesseract to Heimdall. The all-seeing Asgardian used the Tesseract to repair the Bifrost Bridge so the Asgardians could once again protect all of the inhabitants of the Nine Realms endangered by the Marauders.

Later, the Tesseract was locked in the Odin's Vault so nobody could use it again without Odin's permission. The Tesseract was approached by Hela as she was walking in the vault, and she admitted the power of the cube. During Ragnarök, where Loki was about to resurrect Surtur in order to defeat Hela, he decided to take the Tesseract before taking the Crown of Surtur.

Destroyed by Thanos
"We don't have the Tesseract. It was destroyed on Asgard."

- Thor to Thanos

Having located the Tesseract on the Statesman, Thanos and the Black Order traveled with the Sanctuary II and attacked the ship. They killed half of the Asgardian survivors and captured Thor and Loki. Thanos tortured Thor with the Power Stone in order to make Loki give him the Tesseract. Loki acceded to his demands, though he managed to give enough time for Hulk to ambush the Mad Titan but Hulk was swiftly defeated. Afterward, Ebony Maw retrieved the Tesseract and presented it to Thanos, who proceeded to effortlessly crush the Tesseract in his hand and placed the Space Stone in his Infinity Gauntlet.

Capabilities
"If there was any tampering sir, it wasn't at this end." "At this end?" "Yeah, the cube is a doorway to the other end of space right? Doors open from both sides."

- Clint Barton and Nick Fury

The Tesseract is a cube which contains an Infinity Stone, representing the fabric of space. If used correctly, the Tesseract can open gateways to any part of the universe and provide interdimensional travel. Taking the Tesseract physically, Red Skull was suddenly transported to Vormir where the Soul Stone choose him as a Stonekeeper. Thanos was able to manipulate the Tesseract from afar to open a portal that transported Loki to the Joint Dark Energy Mission Facility, which destroyed the facility. Under its influence, Erik Selvig was able to construct a machine powered by the Tesseract guarded by an impenetrable forcefield, which opened an enormous portal to the Chitauri.

Many believe it is an unlimited source of energy because it draws cosmic energy from space. It appears intelligent or temperamental since when Erik Selvig was studying it, he noted that it "behaves". When they turn off power used to harness its energy, the Tesseract turns the power back on using its energy source. Also, the Tesseract was able to recognize Schmidt as "unworthy" to carry the stone what caused the opening of the portal to Vormir. Wherever it is drawing its cosmic power from, it appears to be able to be manipulated from the other endpoint as well. The Tesseract also emitted low levels of Gamma Radiation, which interfered with Selvig's methods of harnessing its energy source, and later allowed S.H.I.E.L.D. to track its movements.

As an incredible source of power, it can be used to power objects and artifacts of incredible power, such as the Bifrost Bridge. A single spark of its power was enough to create a small explosion. HYDRA was able to use the Tesseract to power advanced vehicles and weapons of mass destruction including guns, tanks, and bombs that vaporized their targets. It melted through steel on contact, although it could be held using gloves for a short time, as well as in specialist containment units. It could also be handled directly by exceptionally powerful beings such as Loki, Ebony Maw, and Thanos.

Tesseract Energy
"I think, well, I'm most likely dead on that the Tesseract energy excites plasma with an inverse population of energy levels." "A laser." "A ray of pure energy, two terajoules."

- Leo Fitz and Jemma Simmons

Many people have tried to duplicate the type of energy that the Tesseract emits. The only people known to have successfully harnessed the Tesseract's energy was Johann Schmidt and Arnim Zola, who developed a way to siphon off and store its energy with Tesseract Battery to power weapons. Former HYDRA scientists were able to recreate the power of the Tesseract and created the powerful laser weapon for Peruvian government. Howard Stark managed to discover how to make a similar element that could emit similar energy, but with the technology of his era, he was not able to. Years later, Tony Stark was able to make the element based on his father's research. The element was used as the core for a new Arc Reactor that would stop Stark's Palladium poisoning.

Trivia

 * In the non-canon video game Captain America: Super Soldier, the Red Skull uses the Tesseract to activate the Sleeper, the giant robot buried beneath Castle Zemo.
 * In the comics, the Cosmic Cubes are cube-shaped matrices that can control matter and energy, and allow their users to shape reality. The cubes were used by different species, like the Beyonders, the Kree, the Skrulls and Humans like Red Skull and A.I.M. members.