if you hadn't guessed it already, taking the top spot on this list is the man behind one of the biggest Doctor Who success stories of all time and the show's incumbent Time Lord himself... Mr Peter Capaldi! Peter probably wouldn't have imagined in his most dizziest of daydreams that he would one day take on the role of the universe's coveted defender when he guest appeared as Caecilius in The Fires of Pompeii back in 2008. Fans would later discover that he had once turned down - through fear, more than anything - the chance to audition for the Eighth Doctor but, as a self confessed fanatic, the fact he had been given the opportunity to guest star in the series was probably more than enough at the time. Doctor Who wasn't Peter's only contribution to the Whoniverse before he took over the helm of the TARDIS. He also left his mark on the show's spin off Torchwood when he joined the show - and many would say even stolen it - in 2009 as John Frobisher for its critically acclaimed third series, Children of Earth. Peter's Doctor Who journey has come full circle now but it's only just beginning. His story can be compared to David Tennant's in that Peter has also spent the majority of his life caught under the spell of the Doctor's adventures and not many grow up to enthral generations with their very own portrayal of the coveted Time Lord. With eyebrows like that, it was only a matter of time. What did you think of this list? Are there any other Doctor Who guest stars who returned to the series in bigger roles? Let us know in the comments section below.