Throughout her various incarnations, Velma is usually portrayed as a highly intelligent young woman with highly specific interests in science (which in the Scooby and Scrappy Doo series leads her to pursue a career as a NASA research scientist) or merely being very well read on obscure fields, such as ancient Viking writing. In Scooby-Doo! Abracadabra-Doo, Velma is described by her younger sister Madelyn as being "born with a mystery book in her hand". Consequently, Velma is usually the one to figure out the mystery, sometimes with the help of Fred and Daphne. The Velma character was inspired by the brainy tomboy Zelda Gilroy, as played by Sheila James, from the late 1950s/early 1960s American sitcom The Many Loves of Dobie Gillis.
Source from Wikipeida