...and Tal-Elmar. His name doesn't start with a "G"
, but he was known as Flint-Eye for the spark seen in his eyes when his anger was aroused. I believe that this was a characteristic of the people from whom he was distantly descended from as well. I don't have my books with me, but his story is either in Peoples of Middle Earth or War of the Jewels.
I think it's safe to say that Tolkien subscribed to the notion that "the eyes are the window to the soul" seen not only in all of the afore mentioned angry folk, but also when Gandalf declares that "there was no lie in Pippin's eye" after he interrogated him about the palantir experience.
I personally know very little about Mary-Sues, but agree with Formendacil in that Tolkien had nothing to do with them.