Tesseract

"HYDRA's secret weapon." "Howard Stark fished that out of the ocean when he was looking for you. He thought what we think, the Tesseract could be the key to unlimited sustainable energy. That's something the world sorely needs."

- Steve Rogers and Nick Fury about the Tesseract. The Tessereact (also referred to as the Cube and the Tesseract Cube) is a cube-shaped object that is said to possess unlimited energy itself.

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

- Johann Schmidt

The Tesseract is an ancient Asgardian artifact of unimaginable power. It is unknown when the Tesseract was made, but it was kept in Odin's artifact chamber. In 965 A.D., during their war with the Asgardians, the Frost Giants of Jotunheim, led by Laufey, attacked the planet Earth with the Casket of Ancient Winters. The Frost Giants were eventually defeated, but the Tesseract was lost on Earth, were it was found by Vikings, the inhabitants of Norway. Over the next centuries, the Tesseract was kept safe in a church in the village of Tønsberg. Eventually, 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, Johann Schmidt, the commander of the Nazi special weapons division HYDRA, invaded Norway and found the Tesseract in a box behind Nidhogg in a sculptured mural of Yggdrasil world tree. He took the Tesseract back to his headquarters in the Alps to be experimented on by Doctor Arnim Zola.

After experimenting on the Tesseract, Schmidt and Zola were able to use the object's power to create highly advanced weaponry, fueling Schmidt's plans for world domination. With the power of the Tesseract, Schmidt felt strong enough to turn his back to Adolf Hitler and the Third Reich. He intended to destroy both the Axis and the Allies and make himself ruler of the world.

In December 1943, Schmidt brought the Tesseract into HYDRA's top secret weapons facility in the Austrian Alps, located halfway between Kitzbühel and Klagenfurt. When the Allied Super Soldier Captain America sneaked into the facility and freed 400 Allied POWs, a massive fight began. Seeing that his men won't be able to defeat the freed prisoners, Schmidt took the Tesseract and set the base on self destruction. Before he escaped in the experimental plane, he had a short confrontation with Captain America.

In 1944, shortly after the Allied invasion of Normandy, Schmidt brought the Tesseract to Castle Zemo, an old fortress in Bavaria owned by Baron Zemo. He wanted to use it to activate the Sleeper, a gigantic robotic war machine of unknown origin which was buried beneath the castle for hundreds of years. HYDRA quickly occupied the castle, but Captain America and his Howling Commandos invaded it. Schmidt activated the Sleeper, and the robot destroyed one Allied plane. However, Cap destroyed the Sleeper, which also led to the destruction of the castle. Schmidt again escaped with the Tesseract. In May 1945, with his gigantic super bomber, the Valkyrie, finally finished, Scmidt was ready to launch an offensive that would shake the planet. With its flying nuclear bombs, Schmidt intended to destroy the entire East Coast of the United States. However, his last base was attacked by Captain America, the Howling Commandos, and the US Army detachment led by Colonel Chester Phillips and Peggy Carter of the Strategic Scientific Reserve. Schmidt's men were defeated but he managed to take the Tesseract and flew away in the Valkyrie. However, Captain America managed to board the plane and attacked Schmidt, damaging the machine inside which the Tesseract was held. Angered, Schmidt quickly took the Tesseract and a portal to another realm temporarily opened, pulling Schmidt in as it closed. The Tesseract fell and burned through the floors, causing it to plunge into the sea below. Some time later, it was recovered by Howard Stark – CEO of Stark Industries and a member of the Strategic Scientific Reserve.

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 was one of the founders of S.H.I.E.L.D., an international counterespionage agency. He studied the Tesseract for some time, which stayed in S.H.I.E.L.D.'s possession after his death. At the beginning of the 21st century, Stark's note book with the drawing of a "hypercube", was found and examined by his son Tony.

By 2009, the Tesseract had been in S.H.I.E.L.D.'s possession for some time and the World Security Council ordered S.H.I.E.L.D. to make one of its primary objectives to reignite the Tesseract, a project titled Project P.E.G.A.S.U.S. Nick Fury, director of S.H.I.E.L.D. instead turned his attention to the recovery and surveillance of extraordinary people for a program that would later be called the Avengers Initiative.

After an incident in New Mexico, during which the Asgardian Thor battled and defeated The Destroyer, the humans finally realized they're not alone in the universe. Thor's friend Dr. Erik Selvig was taken to a S.H.I.E.L.D. facility where he met Nick Fury. Fury had a briefcase with the Tesseract inside, stating that it is "power," and asked Selvig if he wanted to study it. Selvig, prompted by Loki, agreed. Fury also positioned Hawkeye in the base to protect 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 After his defeat at the hands of Thor, Loki came into contact with the alien race of the Chitauri and their masters, Thanos and his servant "The Other". Loki promised to retrieve the Tesseract from Earth and give it to them in exchange for their army.

In 2012, Nick Fury was called to the base where the Tesseract was studied by Selvig due to strange activity emulating from the Tesseract, and soon Loki - who had been using Selvig as a conduit to look at Earth - was transported to the base through the interdimensional portal. Loki killed several S.H.I.E.L.D. agents and enchanted Selvig, Hawkeye and a number of other agents into following him. He revealed his plans to use the Tesseract to enslave and rule over the human race. The energy from the portal destroyed the entire nearby area, while Loki took the Tesseract with him to an undisclosed location.

About a year after Fury has recruited Dr. Selvig to study the Tesseract, he has now been notified that it is "misbehaving". Fury arrives at a secret laboratory where Selvig has unknowingly been controlled by Loki into opening a portal into space. The Tesseract activates and transports Loki to the S.H.I.E.L.D. base. Loki immediately begins slaughtering S.H.I.E.L.D. agents and reveals that he plans to use the Tesseract to enslave and rule over the human race.

In response, S.H.I.E.L.D. decided to start the Avengers Initiative, and swayed Bruce Banner, Iron Man, Captain America, and Thor to their cause. Fury also wanted them to trace the Tesseract as it was emitting small amounts of gamma radiation that only they would be able to trace. After escaping from the S.H.I.E.L.D. Helicarrier, Loki ordered Dr. Selvig (now completely under Loki's mind control) to begin to work on the Tesseract to build a device that could transport the Chitauri army to Earth. Selvig and Loki later put the Tesseract-powered device on top of Stark Tower in New York City and activated another portal which opened the door to the Chitauri fleet. Later Natasha Romanoff, instructed by Dr. Selvig, now free from Loki's mind control, used Loki's staff to shut off the portal.

After closing the portal, Thor took the Tesseract back to Asgard along with Loki. Though his superiors were angry at this turn of events, Nick Fury defended his decision to allow Thor to take the Tesseract back to Asgard along with Loki, saying that humanity simply isn't at the level where it deserves the Tesseract's power, much the Council's dismay.