Sesame Street character debuts

The following is a list of known sources for when certain Sesame Street characters made their debut on the show.

Season 1Edit

Big Bird - Debuted in the premiere episode.
Oscar the Grouch - Debuted in the very first episode.
Ernie and Bert - Appeared in the first episode, having previously appeared in the first test pilot.
Kermit the Frog - Appears in the first episode, having already been around since Sam and Friends in 1955.
Cookie Monster - Appears in the first episode.
Grover - Appears in segments known to have debuted during the first season.
Professor Hastings - appears in segments known to have debuted in the first season.
Lefty the Salesman - Appears in segments known to have debuted in the first season.
Roosevelt Franklin and his mother - Appear in segments known to have premiered in the first season.
Little Bird - appears in segments known to have premiered during the first season.
Guy Smiley - Appears in segments known to have premiered in the first season.
Betty Lou - Appears in segments known to have premiered in the first season.

Sherlock Hemlock - A Time Magazine article from 1970 mentions him as a new character in the second season. He made his debut in the second season premiere.
Herbert Birdsfoot - A Time Magazine article from 1970 mentions him as a new character in the second season.
Little Jerry and the Monotones - Their song "Mad" was listed as a Season 2 sketch in Sesame Street: 40 Years of Sunny Days.
Herry Monster
Slimey
Prairie Dawn
Farley

Count von Count - Songs From the Street refers to this as The Count's debut season; He makes his debut in the season premiere.
Sam the Robot - Sam meets Susan and Gordon in the season premiere.

Biff and Sully - Songs From the Street refers to this season as their first appearance.

Telly Monster - Telly moves to the neighborhood in a season ten episode; Sesame Street: 40 Years of Sunny Days lists a clip from this episode as being from that season.

Elmo - Sesame Street Unpaved and the Sesame Street 35 Years Anniversary Game both cite Elmo as making his debut during season 11, as a generic background monster; However, Caroll Spinney has said in his book that the puppet was around in the early seasons, called Baby Monster at the time; He was first called Elmo in season 12, according to a season 12 press kit.

Forgetful Jones and Clementine - A season 12 press kit mentions them as new characters debuting in this season. Buster the Horse is also referred to as a new character, though the puppet had been around since at least 1974.
Warren Wolf - A season 12 press kit refers to him as debuting this year.
Honkers - A season 12 press kit refers to this as the debut season for the Honkers.
Ferlinghetti Donizetti - A season 12 press kit refers to him as a new character this season.
Countess Dahling von Dahling - A season 12 press kit refers to this as her debut season.
Deena and Pearl - A season 12 press kit refers to this as their debut season.
Poco Loco - A season 12 press kit refers to this as his debut season, although he was on the show since at least 1974.
Dr. Nobel Price - A season 12 press kit refers to this as his debut season.
Masha - A season 12 press kit refers to this as her debut season.

Alice Snuffleupagus - Songs From The Street cites 1987 as the year of her debut.

Rosita - Debuted in Episode 2888. Songs From the Street also cite 1991 as her debut year.
Baby Bear - Debuted in in Episode 2909.

Murray Monster - debuts as a nameless monster interviewing kids. He would later get a name during Season 38.

Abby Cadabby - She moves to Sesame Street in the season premiere, after appearing on The Today Show just a few hours earlier.

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