Helga Hufflepuff was the founder of Hufflepuff house at Hogwarts, after whom it is named. Along with three other Hogwarts founders, Helga Hufflepuff helped build Hogwarts castle over one thousand years ago.
At first the four founders worked together, bringing together young witches and wizards to teach them the magical arts. However, one founder – Salazar Slytherin – believed that only those from all-magic families should receive their education at Hogwarts. Hufflepuff, along with the other two founders – Godric Gryffindor and Rowena Ravenclaw – welcomed Muggle-borns into the school, which prompted Slytherin to leave.
During the song performed at the Sorting Ceremony, the Sorting Hat reveals that Helga Hufflepuff valued hard-working students in those she chose for her house. Along with the other founders, Helga helped give the Sorting Hat brains to allow it to sort the students after they were gone.