Ares vs Mars

Ares and Mars
The Greek and Roman gods of war are Ares and Mars respectively. While being similar through their respective pantheons, there are fundamental differences in their representations, more importantly in character.
Both gods are identified with each other as equivalents through Hellenism, but the relationship diverges with how they are portrayed.

Ares was the Greek god of war that would represent the physical force aspect of war. He would be known as bloody, brutal and ruthless, and sometimes it didn't matter which side he fought for, he simply wanted to kill. The Greeks would come to dislike and avoid him, but he was still an important factor in war, as he was the raw force. In comparison, the goddess Athena, Ares' sister, was the goddess of military intelligence and strategy.

Mars on the other hand was the god of war in the Roman pantheon, but was revered and respected in comparison to his unliked Greek counterpart. He is considered a protector of the Roman soldiers, instead of being simply merciless. He is second in importance in the Roman pantheon. This could be because of how the Romans thought of warfare as respected, and was a way to maintain peace (and as an extension, their Empire).

Mars and Ares are both the gods of war, the difference is that Ares is portrayed as a negative and destructive force (while still being a powerful force in war), while Mars is potrayed as a respectable god, the Romans' guardian through military power.