Hades was the Greek God of the Underworld, but not Death. That was the job of Thanatos, who was the God of Death. Interestingly, Thanatos was the brother of Hypnosm, who was the God of Sleep.
For the Romans, Mars started out as the God of Fertility and Growth and the Earth-God, and over time became the God of War, and from there is it was short step to becoming the God of Death.
Below you will find a gallery of inspirational images that will help you in your quest of creating the perfect underworld tattoo.