Summary
The MCU has introduced a number of important magical artifacts over the course of its plethora of movies, but there is perhaps none that has made as many appearances as the Tesseract. First introduced in an end credits scene inThor(and then becoming more prominent inCaptain America: The First Avengerand beyond), the Tesseract plays a big role in the MCU, particularly in the first phase. It comes back in the later part of the Infinity Saga as well, as it rises to even greater importance as an Infinity Stone.
Of course, this object didn’t start as an Infinity Stone, rather, it was actually based on the Cosmic Cube from Marvel comics. This has led to some confusion about the true nature of the Tesseract in the MCU. Marvel hasn’t always been super clear about what exactly it does or what its true power scope is, which has made some fans confused aboutwhat role the Tesseract serves. Is it just the Cosmic Cube, or is it one of the Infinity Stones as well?

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How Was The Tesseract Made?
When talking about the Tesseract, there are a couple of sources to consider that change its story. The Tesseract in the MCU is different from the comics version, so the origin story differs a little. In the MCU, the Tesseract was created at the beginning of the universe as the six singularities were formed into the Infinity Stones. The Tesseract acted as a vessel for the Space Stone, so that the stone could be used by different peoples and civilizations over the course of history. It then cameinto the care of the Asgardiansand was locked away in Odin’s vault until Odin brought it to Earth to be kept safe in a church in the village of Tønsberg (where it was then subsequently stolen by Red Skull).
In the comics, however, the Tesseract was created by cosmic beings called the Beyonders. They are a race of god-like with great power who can even affect the fabric of reality. The Tesseract (or the Cosmic Cube) was the tool they created in order to harness the extent of their powers and control the universe. Its primary function was “wish-granting” and reality warping, and it was powerful enough tocause multiversal chaosat one point, though the majority of its effects otherwise were usually just illusions.

What Are The Tesseract’s Powers?
Because it contains the Space Stone, the Tesseract seemingly has an immense amount of power, though the exact parameters are a bit confusing. The Tesseract can open wormholes to any part of the universe, thereby allowing interdimensional travel. When Red Skull touched the Tesseract directly, it transported him to Vormir. Loki also used its teleportation abilities when he used the Mind Stone (in his scepter) to remotely access the Tesseract on Earth and created a portal with it. Erik Selvig used it to create the giant wormhole over New York that lets the Chitauri throughinThe Avengers.
It appears that it has basically an unlimited amount of energy as it draws on cosmic energy from space. As such, it could be used to power objects on a large scale, such as the Bifrost. Mar-Vell had a Tesseract-powered Light Speed Engine, and when it exploded, the cosmic force hit Carol Danvers and gave her the power to manipulate energy, transforming her into Captain Marvel. HYDRA also used the Tesseract to power its vehicles and weapons. Most people who attempted to handle it had to use special equipment or gloves, unless they werea being of great powerlike Loki, Captain Marvel, or Thanos (or Goose the cat, of course).

Is The Tesseract The Cosmic Cube Or The Space Stone?
The answer to this is a little complicated, as the answer is both, sort of. As previously mentioned, the MCU changed the Tesseract intoa vessel for an Infinity Stone, as that fit better with the direction of the overarching story they were trying to tell. It initially started with a function closer to that of its comics counterpart, but it evolved as time went on. As of this moment in the Marvel Cinematic Universe, the Tesseract is what holds the Space Stone, so it’s definitely more of an Infinity Stone than anything else.
This wasa smart decision by Marvel, as keeping the Tesseract as the Cosmic Cube may have made it a bit overpowered. The Cosmic Cube has nearly limitless power, and that would have been a really hard thing to write around in the MCU. Making it an Infinity Stone not only helps move the plot along as more Infinity Stones are introduced throughout the universe as the Infinity Saga went on, but it also limits its function to something that is much easier to work with, and doesn’t create complications within the plot.