Missing Link Doo is an ancestor of the Doos. His name would suggest that he was the first in the Doo family to have anthropomorphism.
A Pup Named Scooby-Doo
Professor Digmi disguised himself as Nasty-Doo, and made up a curse to scare the Doos away from Doo Manor, so he could find the skeleton's missing leg bone, which would've made him famous. However, when he was captured by the gang, Velma Dinkley found the leg bone and connected it.