The Letters of the Alphabet have long been an important part of Sesame Street, as a collection of sounds or as concepts and as sponsors of individual episodes (along with numbers). The alphabet has often had physical presence on the street as well. Though often included via superimposed titles, background signs, or large props, the Letters have frequently functioned as characters in their own right. In early sketches, this was accomplished in a more simplistic fashion, such as the skit in which a foam, undecorated Letter W, operated on visible rods, would slowly sidle up to Kermit the Frog and begin to pummel him.
Later on, the Letters would become more than living props, but would gain faces, voices, and even personalities.