Thelma is a marine biologist, and Velma Dinkley's aunt.
Physical appearance
Like Velma, she also has brown hair and wears glasses.
Personality
Takes her job as a marine biologist at the Coolsville Marine Institute very seriously. She loves her pet dolphin Skipper very much, and is rather concerned for her safety and the other dolphins that were stolen. Like Velma, she also seems to know what might be what.
History
A Pup Named Scooby-Doo
Season one
She was concerned about her missing dolphins. One of them, Skipper, always came to her calls, and then she realized someone was stealing her dolphins.