Who in "To Kill a Mockingbird" is considered the filthiest human with a dark gray neck?

Burris Ewell is known as

"the filthiest human [Scout] had ever seen.  His newck was dark gray, the backs of his hands were rusty, and his fingernails were black deep into the quick.  He peered at Miss Caroline from the fist-sized clean space on his face."

Burris is the boy who only attends the first day of class and then never comes to school again.  He is the first of the Ewells that we meet.  The rest of the story is based around Mayella's (his sister) accusations on Tom Robinson and her father's (his dad) behavior and relationship with those in Maycomb.

This description happens in chapter 3 at school.