The earliest trace of Kermit first appeared in 1955 on WRC-TV's Sam and Friends. This prototype Kermit was created from a discarded spring coat belonging to Henson's mother and two ping pong ball halves for eyes.
Initially, Kermit was a lizard-like creature. He subsequently made a number of television appearances before his status as a frog was established. His collar was added at the time to make him seem more frog-like and to conceal the seam between his head and body.
The origin of Kermit's name is a subject of some debate. It is often claimed that Kermit was named after Henson's childhood friend Kermit Scott, from Leland, Mississippi. However, Karen Falk, head archivist and board of directors member for the Jim Henson Legacy organization, denies this claim on the Jim Henson Company's website:
While Jim Henson did have a childhood acquaintance named Kermit, it was not an uncommon name at the time, and Jim always said that the Frog was NOT named after this child from his elementary school.
Joy DiMenna, the only daughter of Kermit Kalman Cohen who worked as a sound engineer at WBAL-TV during Jim Henson's time with Sam and Friends, recalls that the puppet was named after her father. According to Kermit Cohen's obituary, as well as DiMenna and Lenny Levin, a colleague of Mr. Cohen's at WBAL:
The late puppeteer had been the host of a show, "Sam and Friends," at WRC-TV in Washington when he was invited to tour WBAL's studios. Both were NBC affiliates then, and WBAL carried the show, Mr. Levin said.
Mr. Henson was introduced to members of the sound and camera crew, including Mr. Cohen.
"When he heard his name, Jim turned around, snapped his fingers and said to his wife, 'That's what we call the frog – Kermit.'
Another common belief is that Kermit was named for Kermit Love, who worked with Henson in designing and constructing Muppets, particularly on Sesame Street but Love's association with Henson did not begin until well after Kermit's creation and naming, and he always denied any connection between his name and that of the character.
As Sesame Street is localized for some different markets that speak languages other than English, Kermit is often renamed. In Portugal, he is called Cocas, o Sapo (sapo means "toad"), and in Brazil, his name is similar: Caco, o Sapo. In most of Hispanic America, his name is la rana René (René the Frog), while in Spain, he is named Gustavo. In the Arabic version, he is known as Kamel, which is a common Arabic male name that means "perfect". In Hungary, he is called Breki (onomatopoetic).
Jim Henson originated the character in 1955 on his local television series, Sam and Friends. Brian Henson described his father's performance as Kermit as "coming out of his own personality—was a wry intelligence, a little bit of a naughtiness, but Kermit always loved everyone around and also loved a good prank." He continued to perform the character until his death in 1990. Henson's last known performance as Kermit was for an appearance on The Arsenio Hall Show to promote The Muppets at Walt Disney World. Henson died twelve days after that appearance.
Following Henson's death, veteran Muppet performer Steve Whitmire was named Kermit's new performer. In 2017, Whitmire seemed to imply in a blog post that Jim Henson had asked him to assume the role before he died, though Jim's daughter Cheryl Henson claimed Brian had selected him after Jim's death. Whitmire's first public performance as Kermit was at the end of the television special The Muppets Celebrate Jim Henson in 1990. He remained Kermit's principal performer until 2016. Disney announced that Matt Vogel would be taking over as the performer and voice for Kermit on July 10, 2017. Whitmire later revealed that he had not chosen to voluntarily leave the role, but rather, had been recast by Muppet Studios in October 2016. In an interview with The Hollywood Reporter later in July 2017, Whitmire elaborated he was fired for two reasons: long-term creative disagreements over Kermit's characterization and prolonged labor union negotiations that delayed his involvement in Muppet-related productions.
For a brief demonstration at MuppetFest (a 2001 Muppet fan convention), Muppet performer John Kennedy performed Kermit opposite Whitmire's performance of young Kermit (from Kermit's Swamp Years). Kennedy also performed Kermit for Muppets Ahoy!, a 2006 Disney Cruise Line stage show (though Whitmire performed Kermit for the first few shows). Muppet performer Artie Esposito briefly performed Kermit in 2009 for a few personal appearances (an appearance on America's Got Talent, the MTV Video Music Awards, and at the 2009 D23 Expo).
Voice actor Frank Welker provided the voice of Baby Kermit on the animated Saturday morning cartoon, Muppet Babies. He also provided the voice of an adult Kermit for a short-lived spin-off, Little Muppet Monsters. Matt Danner voices Baby Kermit on the 2018 reboot of Muppet Babies.
A biography has been developed for Kermit the Frog as if he was an actual living performer rather than a puppet character. According to this fictional biography, he was born in Leland, Mississippi alongside approximately 2,353 siblings, though a 2011 "interview" on The Ellen DeGeneres Show has him state that he was from the swamps of Louisiana.
As portrayed in the 2002 film Kermit's Swamp Years, at the age of 12, he was the first of his siblings to leave the swamp, and one of the first frogs to talk to humans. He is shown in the film encountering a 12-year-old Jim Henson (played by Christian Kriebel) for the first time.
According to The Muppet Movie, Kermit returned to the swamp, where a passing agent (Dom DeLuise) noted he had talent and, thus inspired, he headed to Hollywood, encountering the rest of the Muppets along the way. Together, they were given a standard "rich and famous" contract by Lew Lord (Orson Welles) of Wide World Studios and began their showbiz careers. In Before You Leap, Kermit again references encountering Jim Henson sometime after the events depicted in the course of The Muppet Movie and details their friendship and their partnership in the entertainment industry, crediting Henson as being the individual to whom he owes his fame. At some point after the events of The Muppet Movie, Kermit and the other Muppets begin The Muppet Show, and the characters remain together as a group, before starring in the other Muppet films and Muppets Tonight, with Kermit usually at the core of the stories as the lead protagonist. Kermit is shown in The Muppet Movie as stating that the events of the film are "approximately how it happened" when asked by his nephew Robin about how the Muppets got started.
Fozzie Bear is portrayed as Kermit's best friend—a fact reiterated by Kermit in Before You Leap—and the two were frequently seen together during sketches on The Muppet Show and in other Muppet-related media and merchandise.
On August 4, 2015, Kermit the Frog and Miss Piggy "announced" that they had ended their romantic relationship. On September 2, 2015, Kermit was stated to have found a new girlfriend, a pig named Denise, but around February 2016, Denise supposedly broke up with Kermit after almost six months together.