The first Unicorn (Milos Masaryk) debuted in Tales of Suspense #56 (Aug. 1964) and was created by Stan Lee and Don Heck.

[1] Milos Masaryk was a Soviet intelligence agent assigned to track down the original Crimson Dynamo, who defects to America.

[2] The Unicorn was among the villains affected by Doctor Doom's high-frequency emotion charger, and was compelled to attack the Fantastic Four at the wedding of Reed Richards and Susan Storm.

[6] The process left the Unicorn with "accelerated cellular deterioration", and he is taunted with a cure by the Red Ghost in exchange for assistance against Iron Man.

The process has the result of driving Masaryk insane, and a disorientated Unicorn inadvertently activates the hidden robot Arsenal.

Still insane, the Unicorn refuses to believe that "The Other" was a lie, and begins to walk back to the Soviet Union via the ocean to find him.

[17] A second unnamed (at the time of his debut) Unicorn with a developed tentacled eye within his power-horn appears as a member of Remont 4 and goes on a rampage in Saint Petersburg until captured by the third Titanium Man.

[21] A third Unicorn, whose real name is Aaidan Blomfield and wore the same Unicorn costume as his predecessors, only with an actual horn on the helmet, is recruited into the supervillain group Stockpile by Morgan Stark to destroy Iron Man, but they are defeated by the combined efforts of Iron Man and War Machine.

The Unicorn's soft tissues are dozens of times harder than those of an ordinary human, making him highly resistant to physical injury.

The process which endowed the Unicorn with superhuman powers caused accelerated cellular deterioration, which eventually severely affected his sanity and physical health.

This version was a convict who participated in an abandoned Russian super-soldier program involving the Vision's biotechnology and went insane due to years of isolation.