c. 1300 as the name of the bright reddish-orange planet in the heavens; late 14c. as the name of the Roman god of war, from Latin Mars (stem *Mawort-), the Roman god of war (identified with Greek Ares), a name of unknown origin, apparently from earlier Mavors, related to Oscan Mamers.
According to Watkins the Latin word is from *Mawort- "name of an Italic deity who became the god of war at Rome ...." He also had agricultural attributes, and might ultimately have been a Spring-Dionysus. The planet was so named by the Romans, no doubt for its blood-like color. The Greeks also called the planet Pyroeis "the fiery." Also in medieval alchemy, "iron" (late 14c.). The Mars candy bar was first manufactured in 1932 by Forrest Mars Sr. of the candy-making family.