Short answers, pulled from the story.
The Plastic Ono Band was an English rock band and Fluxus-based artist collective founded by John Lennon and Yoko Ono in 1968-69. Ono originally conceived the name in 1967 as an idea for an art exhibition in Berlin, envisioning an open-ended conceptual group with no fixed membership.
The Plastic Ono Band released their first single, "Give Peace a Chance" backed with Ono's "Remember Love," on the 4th of July 1969. It was recorded during Lennon and Ono's second Bed-in for Peace, held in Montreal in late May and early June 1969.
The Plastic Ono Band had a rotating line-up rather than a fixed roster. Frequent members included Eric Clapton, Klaus Voormann, Alan White, Billy Preston, Jim Keltner, Ringo Starr, George Harrison, and Keith Moon. From 2009, the revived Yoko Ono Plastic Ono Band was led by Ono and her son Sean Lennon.
Live Peace in Toronto 1969 was the first LP credited to the Plastic Ono Band, recorded at the Toronto Rock and Roll Revival festival on the 12th of September 1969. Lennon assembled the band with less than twenty-four hours' notice after festival organizer John Brower called to invite him to attend; Lennon offered to perform instead.
Studio albums credited to the Plastic Ono Band include John Lennon/Plastic Ono Band and Yoko Ono/Plastic Ono Band (both released the 11th of December 1970), Some Time in New York City (1972), Between My Head and the Sky (2009), and Take Me to the Land of Hell (2013). The live album Live Peace in Toronto 1969 was the first LP released under the name.
Yoko Ono revived the Plastic Ono Band in 2009 with the EP Don't Stop Me! and the album Between My Head and the Sky. The revived group, credited as the Yoko Ono Plastic Ono Band, continued performing live concerts until 2015 and released a final studio album, Take Me to the Land of Hell, in 2013.