TV URBAN LEGEND: Captain Jack Harkness was contractually not allowed to appear in Doctor Who once Steven Moffat took over the series.
One of the most popular supporting characters introduced by Russell T. Davies when he rebooted Doctor Who in 2005 (after the series had been off the air for a number of years) was Javic Piotr Thane, a time agent from the 51st Century played by John Barrowman, who was best known by the alias he was introduced under, Captain Jack Harkness.
Captain Jack was a major supporting player in the first four seasons (or "series") of Doctor Who, working with both the Ninth Doctor (Christopher Eccleston) and the Tenth Doctor (David Tennant).
Captain Jack appeared in Russell T. Davies' final episode of Doctor Who (the Series 4 Finale) and then Davies introduced a spin-off series called Torchwood, which starred a group of agents who help protect the world from aliens. Captain Jack was the head of the team.
Harkness has not appeared on Doctor Who since Davies left the series, and so reader Christopher V. wrote in to ask, "As show runner for Doctor Who, was Steven Moffat contractually prohibited from using characters created by Russell T Davies, such as Captain Jack Harkness or Torchwood?"
That does not appear to be the case. While discussing the fact that he did not believe that the Doctor (then played by Matt Smith) should appear on Torchwood since Torchwood was aimed at a more adult audience than the more all-ages Doctor Who, Moffat noted "The Doctor could never go to Torchwood. [Torchwood executive] Russell [T Davies] and I both agree on that. Doctor Who has a tremendous relationship with children in Britain. They'd want to watch Torchwood then, and it's not really a children's show."
However, Moffat then noted that he planned on bringing in Captain Jack for a then-recent episode of Doctor Who. He explained, "I'd have [brought back Captain Jack] for 'A Good Man Goes To War', but John was busy doing Miracle Day... When we've got a good story, we'll do it. You can't just bring somebody back and say, 'That's a story'. I won't be thinking, 'How do you bring Captain Jack back?' I'll be thinking, 'You know what this needs? We need to bring Jack back for it'."
Thus, it seems pretty clear that Moffat had not specific inability to use Captain Jack, it just did not work out during his stint on the series.
Therefore, the legend is...
Thanks to Christopher for the suggestion!
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