Mars, equivalent of the Greek Ares, is the god of war and as such sits in full armor on his chariot (which admittedly doesn't look that warlike in this card).
One might easily assume that Mars found his way into traditional Tarot in the Chariot trump VII, as the cards strongly resemble each other.
The strange looking dog on the card was most likely meant to be a wolf, as the wolf was the sacred animal of Mars.
Further reading: Mars (Planets)