Mark Sheppard and five others have been added to the line-up of Doctor Who Convention, BBC Worldwide announced today. The actor, who played the role of Agent Canton Delaware III in the opening episodes of Doctor Who’s sixth series, has appeared in a number of perennial science fiction shows, including “Firefly” and “Supernatural”.

The other additions are as follows: Nick Briggs, voice of the Daleks; Neil Gorton, a visual effects specialist from MillenniumFX; Ian McNeice, who portrayed Winston Churchill; and Raquel Cassidy, who played Cleaves in The Almost People and The Rebel Flesh. They join a list of appearances already including Matt Smith, Steven Moffat, and Arthur Darvill.

“I grew up watching Doctor Who, and the fans are a huge part of what really makes the show so very special,” Sheppard is quoted as saying. “I can’t wait to come back to Cardiff for this unprecedented behind-the-scenes event - a unique chance for fans to meet the amazing people responsible for so much of the show we all love and get to experience their talent and creativity in a totally new way.”

More line-up announcements are on the way, according to the BBC, which will surely make Doctor Who Convention an unmissable event. The pyrotechnics demonstrations, makeup masterclasses, live Q&A sessions, and the limited TARDIS set tour are just some of what’s in store for attendees. Find out more on the official Doctor Who Convention website here.