Why did Billie Piper leave Doctor Who after the second season, only returning occasionally since? It's easy to forget that showrunner Russell T. Davies was originally seen as taking something of a risk when he cast Billie Piper as the Doctor's first companion in his Doctor Who relaunch in the mid-2000s. Piper was best known as a pop-star and had only recently begun her acting career.
It didn't take long for Piper to win any critics over, though. In large part that was due to skillful writing and directing, with her character Rose Tyler becoming unusually well fleshed-out. The dynamic between Piper's Rose and Christopher Eccleston's Doctor was particularly good, with Rose helping the Doctor deal with his grief and survivor's guilt. When David Tennant stepped in as the Tenth Doctor, he and Piper quickly established a strong rapport. The two actors were utterly comfortable with one another, and their friendship showed on the screen as well. And yet, there were constant - and often conflicting - reports that Piper was considering quitting Doctor Who.
While Rose was great in Doctor Who, behind the scenes, Billie Piper was going through a difficult time. She was still recovering from her battle with anorexia, and her marriage to British television personality Chris Evans ended in divorce. Meanwhile, she found Doctor Who was becoming pretty overwhelming. The seasons were long and the filming process was arduous; even when the show had wrapped up production, she found that Doctor Who was dominating every conversation. In the end, in 2006 Piper decided she'd leave once the second season had been completed.
Piper has always insisted she still loves the show, and was linked with a Doctor Who return last year, but she simply wanted to do something different. Piper used her newfound celebrity as a Doctor Who companion as a launchpad, swiftly taking on a starring role in ITV2's The Secret Diary of a Call Girl. Meanwhile, she also wrote a startlingly open and honest autobiography called Growing Pains, which was published shortly after she left Doctor Who.
Nowadays, Doctor Who is bigger than ever before, and as a result she keeps on coming back. Piper returned to Doctor Who in "The Day of the Doctor", and she's recently worked with Big Finish on some audio adventures charting Rose Tyler's journey across the Multiverse. To her delight, this has even presented Piper with an opportunity to work with Russell T. Davies again, as he helped the team develop the scripts for the stories. Big Finish is well-known for building up strong relationships with the actors they work with, so it will be fascinating to see what comes next for Billie Piper.