Joining JK Rowling's creations on first class stamps in the series are failed student Rincewind and witch Nanny Ogg, from Terry Pratchett's Discworld books.
Aslan the Lion and the White Witch, from CS Lewis's Chronicles of Narnia, feature on other stamps in the series.
The Arthurian figures of wizard Merlin and Morgan le Fay make up the set.
Sir Michael Gambon and Ralph Fiennes appear in character on the Potter stamps in images taken from the successful movie franchise.
The Narnia stamps also use images from the recent film versions, with Tilda Swinton pictured as the White Witch.
According to its website, Royal Mail commissioned research from experts in British folklore and cultural history to determine the most appropriate characters.
"It soon became obvious that most of these tales, whether ancient or modern, involved more than one magical character," a posting reads.
"It was decided to look at four different sets of stories and extract two characters from each."