From Homestar Runner Wiki
The Sneak (a.k.a. "The Dapper Swindler") is the Old-Timey version of The Cheat, and takes the appearance of an opossum. He is always silent (save for when delivering a telegram) and communicates by waving his nose. He's the Strong Man's greatest pal, and loves to join Old-Timey Strong Bad in causing catastrophe. His schemes include dropping The Homestar Runner from his "flying machine", stealing fresh jam and putting a Bengal tiger in The Kaiser's latrine. He supposedly likes to do the hully gully on the Panama Canal, but has only been seen doing it on a barrel. The a cappella group DaVinci's Notebook wrote a song for him, entitled the Ballad of The Sneak, which was made into a cartoon by The Brothers Chaps. The lyrics in the song suggest that The Sneak is yellow in color, similar to his present day double, despite the fact that the Old-Timey cartoons have no color.
"The Dapper Swindler" is the nickname given to The Sneak on his wanted poster. When he was spotted in Tammany Hall, police sketch artists made a questionable rendering of the infamous knave as a human figure with The Sneak's nose and fangs. The poster mentions that he is known as The Sneak in the Northwest Territories.