Doctor Who: 14 Cool Details Revealed In Steven Moffat's Wedding Of River Song Commentary
11. Dorium Returned Because Of A Recommendation From A Previous Director
Dorium Maldovar first appeared in Series 5's The Pandorica Opens, with the character selling a vortex manipulator to River Song in a very short scene.
He then popped up again in Series 6's A Good Man Goes To War, as one of the Doctor's allies during the raid on Demon's Run. During this episode, he gets beheaded by the aptly-named Headless Monks, which led to his third and final televised Who appearance in The Wedding Of River Song - where his severed head is in a box.
From the sounds of it though, Moffat originally didn't have plans to bring him back for a second time, let alone a third.
During the commentary, the writer states that actor Simon Fisher-Becker was so good while filming The Pandorica Opens (apparently, he "just got it"), that director Toby Haynes said that Dorium must return in a future episode, and Moffat, clearly, took this recommendation seriously.