Mitras

Mitras is a non-Norse God mentioned very briefly in the Dragons: Riders of Berk comic, "The Legend of Ragnarok".

Mythology
Mitras appears to be a male god originating with historic cultures in Northern India, and then spreading to the Iran area, and later adopted by the Greeks and Romans. His name translates to contract in Sanskrit. There is some contention amongst historians whether the Indo-Iranian God is the same as the Greco-Roman one, or the name was merely borrowed from earlier cultures.

Mitras is the protector of treaties, and was often invoked when forming treaties. Later, he was associated with truth, and later still with the Sun.

The cult of Mithras - Mithraism - evolved with the Greek and Romans. This secretive worship centered around Mitras' connection with the sun. Common artwork seen connected with Mithraism is the Tauroctony - the killing of a sacred or sacrificial bull. The worship of Mitras spread throughout Roman-held Europe, however, there is no evidence that the Norse picked up this deity for their pantheon.

Dragons: Riders of Berk Comics
In "The Legend of Ragnarok", trying to take advantage of the dangerous seas around Berk, Alvin and the Outcast secretly sneak up to Berk from the sea. Unknown yet to the humans, the Purple Death is awakened from under the sea near the Isle of Berk. Alvin's landing party is destroyed by some thing in the water. As an unnamed Outcast sailor flies through the air, he utters, "Mitras wept". It is unclear why he was referring to this God.