Zoe is the orange 3-year-old female monster described as Elmo’s best friend.
Zoe was introduced to Sesame Street in 1993 as part of an effort to add more prominent female Muppet characters. She is energetic, confident, imaginative, and especially enthusiastic about singing and dancing. Her personality is often presented as both dainty and strong-willed, giving her a distinctive place among the show’s young monsters.
Her friendship with Elmo is a recurring part of the program. The two are close in age and frequently play, imagine stories, and work through disagreements together. Zoe also has a pet rock named Rocco, whose presence creates comic misunderstandings—particularly when Elmo becomes frustrated that Zoe treats a rock as if it were alive.
Viewers sometimes confuse Zoe with Rosita because both are female monster characters. Rosita is turquoise, bilingual in English and Spanish, and generally associated with music and guitar playing. Julia is another important friend in Elmo’s world, but she is a human-like autistic Muppet character rather than the orange monster identified in this question.