Sonja Kristina

In 1968, Kristina auditioned for and won the part of "Crissy" in the London stage production of the stage musical Hair. She features on the original cast album singing the song "Frank Mills", also released as a single. She also briefly sang with The Strawbs, following the departure of Sandy Denny. Dave Cousins remembered:

According to AllMusic, it was Galt McDermott, who wrote the music for Hair and another musical Who the Murderer Was, who employed the four members of Curved Air as a house band, who suggested when the stage show closed that they add Kristina to the line-up. Another version has it that manager Mark Hanau had the idea Kristina's alto vocals could become a vital ingredient in a new band. On 1 January 1970, the singer received an official invitation to become a member of Curved Air. She remembered sitting backstage on the theatre stairs listening to a cassette of the band's music Hanau had given her, and being much impressed. Described by Sting as a "real beauty, otherworldly and unattainable", Kristina played a full creative role bringing with it a powerful female sexuality. Her experiences working as a croupier in the London Playboy Club during the early 1970s, reflected itself in the stage persona she later developed.

In 1971, Kristina received the Sounds magazine Top Female Vocalist Award, and in 2014 the 'Guiding Light Award' at the Progressive Music Awards. The award was presented by television broadcaster, and long-standing Curved Air fan, Katie Puckrik for helping pave the way for other female artists who followed, including Kate Bush, Heather Findlay, Anne-Marie Helder and others.

Kristina married Malcolm Ross in 1971 and Stewart Copeland in 1982, with whom she had three sons: Sven (Kristina's son from a prior relationship, who Copeland adopted), Jordan (of Hot Head Show) and Scott. She became acquainted with Copeland while he was first road manager and then drummer for Curved Air (1974–1976). They divorced in 1991.

After Curved Air, she returned to Hair. She has also performed solo, including as part of the acid folk movement in London in the early 1990s, culminating in her critically acclaimed Songs from the Acid Folk in 1991, and in a multi-media duo MASK, with Marvin Ayres.

Cousins eventually published the book, called The Bruising of Hearts, The Losing of Races, in 1993. It included a poem "Silver Smile", written for Kristina in the late 1960s.

In 2008, Curved Air was reformed with other original members including Darryl Way and Florian Pilkington-Miksa and, later, Kirby Gregory from the Air Cut line up. The band continues to record and perform internationally.