X is the 24th letter of the English alphabet. Used in various Sesame Street sketches as a prop or concept, the Letter X has also appeared as a Muppet character on multiple occasions, such as being serenaded by Patti LaBelle or as a mystery guest on Mystery Guest.

The letter first sponsored Episode 0004.

Songs about X

• "X Marks the Spot!"
• "Oh, How I Miss My X"

Sketches about X

• The Typewriter: X - X-ray
• Human letters at the Beach (EKA: Episode 3725)