Like Truxton, Eugene, Tomba, Bonk, and Judge, he is a hellhound. But instead of being black and white with colored markings, his fur is light gray.
It is also unclear whether his real name is Sullivan or Rosewell. Squeedge once posted a drawing of him on her Tumblr account claiming his name is Sullivan, while on other websites his name is Rosewell. 
On July 26th, 2017, Rosewell was up for sale on Squeedge's Toyhou.se account and was claimed by whisski.