What is the Race of Darth Maul?
Maul's Race is listed in the textbooks only as "humanoid." A member of the Jedi Council is the same race as Maul, or a very close relative. This Jedi's name is Eeth Koth. His race is Iridian Zabrak.
More information on Darth Maul can be found here. More information on Eeth Koth can be found here.
What are the Markings on Darth Maul's Face?
The power of the Dark Side wells from anger and preys on fear. Thus Maul has insigniated himself, via "tattoos," with classical symbols of fear such as forked tongue, fearsome eyebrows, devilish red appearance, skeletal outlines, etc. I am not sure if his tooth decay is also intentional.