In both the anime and the manga, the Titans appear completely naked, though this isn't all that offensive since they are portrayed as not having any sexual organs. However, due to censorship laws, the Malaysian version of manga portrays the Titans as wearing pants.
The manga artist, Hajime Isayama, got the idea for the Titans when he encountered a drunk customer at a coffee shop he worked in. He was inspired by the inability to communicate and realised the most dangerous thing was the human race.
Aspects of Levi's design and personality were based on Rorschach from Watchmen.
Isayama has been vocal for his love of shows like Game of Thrones and Breaking Bad. He even revealed that Falco Grice is based on Jesse Pinkman, played by Aaron Paul. The show's Saul Goodman, as well as many Game of Thrones characters even made "cameos" in the manga where they appeared as Titans.
Isayama has stated that part of the reason he chose the name "Eren" for the character is because it sounds feminine, which would make it easier to remember.