Sameth, often shortened to Sam, is a Prince of the Old Kingdom. His father, Touchstone, is the King, while his mother is the Abhorsen. His sister, Ellimere, is heir to the throne. Although he is initially thought to be the Abhorsen-in-waiting, it is discovered at the end of Lirael that his aunt Lirael has the Abhorsen's blood in her veins, and so Lirael then becomes the Abhorsen-in-waiting and Sam is revealed to be a descendant of the Wallmakers. At the second binding of Orannis, Sam stands for Belgaer.
Other than that, Sameth (like Touchstone in Sabriel), becomes a close companion of Lirael, and helps her later in the third part of the second book, they both are accompanied by the free magic cat Mogget and the Disreputable Dog.