According to Rabbi Yehudah, the Tachash was a magnificent multi-colored (6 colors total) animal, which lived in the desert and whose hide was used to make the covers of the Mishkan. It had a single horn in the middle of its forehead.
The Tachash only existed at that time and has been extinct ever since. According to Rabbi Nechemiah, the Tachash was created specifically for the construction of the Mishkan’s and ceased to exist immediately afterwards.
There is a dispute whether the Tachash was a kosher animal or not.
The animal sacrificed by Adam HaRishon was also a one-horn kosher animal.
Some say that the clothing God made for Adam and Eve, were from the Tachash.