"And you think we're scum, do you? Scum who'll come running when the Ministry tells 'em to? See this [ring]? Centuries it's been in our family, that's how far back we go, and pure-blood all the way! Know how much I've been offered for this, with the Peverell coat of arms engraved on the stone? See this [locket]? Salazar Slytherin's! We're his last living descendants, what do you say to that, eh? So! Don't you go talking to us as if we're dirt on your shoes!"
-- Marvolo Gaunt (HBP10)
Marvolo is the patriarch of the Gaunt family, such as it is. He shorter than his son Morfin, with odd proportions. He has “bright brown eyes, short scrubby hair, and wrinkled face.” Harry think he looks like a powerful, aged monkey (Salazar Slytherin is also described as “monkey-like” in CS17). Marvolo wore a gold ring with the Peverell coat of arms carved into a black stone (HBP10).
Marvolo attacked Ministry personnel who had come to arrest his son, so he too was arrested. He was convicted by the Wizengamot and sentenced to Azkaban for 6 months (HBP10). He died before his son's sentence was complete.
"gaunt" = lean and haggard, especially because of suffering, hunger, or age.