Fripp and Sinfield recorded the second King Crimson album, In the Wake of Poseidon, in 1970 with the Giles brothers hired back as the session rhythm section, and with jazz pianist Keith Tippett and Circus saxophonist Mel Collins as guest musicians. The group considered hiring Elton John to be the singer, but decided against the idea. Lake then agreed to sing on the album in exchange for receiving King Crimson's PA equipment, except on "Cadence and Cascade", which is sung by Fripp's friend Gordon Haskell. Though Tippett was offered band membership, he preferred to remain as a studio collaborator, performing with the band for a single gig. Upon its release in May 1970, In the Wake of Poseidon reached No. 4 in the UK and No. 31 in the US. It received some criticism from those who thought it sounded too similar to their first album. With no musicians to perform material from their new album, Fripp and Sinfield persuaded Haskell to join as singer and bassist and recruited Andy McCulloch as drummer, retaining Collins as saxophonist, flautist and occasional keyboard player.
During the writing sessions for the third album, Lizard, Haskell and McCulloch had no say in the direction of the material, since Fripp and Sinfield wrote the album themselves, bringing in Tippett, Mark Charig on cornet, Nick Evans on trombone, and Robin Miller on oboe and cor anglais as additional musicians. Haskell sang and played bass. Jon Anderson of Yes was also brought in to sing the first part of the album's title track, "Prince Rupert Awakes", which Fripp and Sinfield considered to be outside Haskell's range and style. Lizard featured stronger avant-garde jazz and chamber-classical influences than previous albums, as well as Sinfield's upfront experiments with processing and distorting sound through the EMS VCS 3 synthesiser. It also featured complex lyrics from Sinfield, including a coded song about the break-up of the Beatles, with almost the entire second side taken up by a predominantly instrumental chamber suite describing a medieval battle and its outcome.