Not much about his personality is known, but he was furious upon being fired, so much that he vowed to come back for vengeance.
Daphne's great-grandfather hired him as a chef. But they had an argument and Goulash was dismissed. But he swore that he would return, and steal from the Blake's. This happened so long ago that the man presumably died.
A Pup Named Scooby-Doo
Mr. Gordon used this story as the basis for his disguise as the Ghost of Chef Pierre Goulash to steal from the Blakes. And he loaned the gang Robopup for them to be lead on the wrong trail, but his plan was foiled. (Robopup)