Shatner, who starred as Captain James T. Kirk in the original Star Trek series, joined forces with the other five Star Trek TV captains at the convention at London's ExCel center, the first live Star Trek event in Britain for more than a decade.

"There are a lot of people travelling from all over the world to come here. It's sort of monumental in its worth," said Shatner, who has also won an Emmy for his role in the U.S. drama Boston Legal.

"I enjoy meeting fans on a broad scale. There are 17,000 people...coming to this convention, it's a huge event."

There was a time, however, when Shatner did wonder what motivated Star Trek fans to flock to conventions, splashing out on merchandise and dressing up in replica costumes true to the series' humble beginnings.

In 1986 Shatner starred in a "Saturday Night Live" sketch, in which he told a convention full of awe-struck Star Trek fans to stop wasting their lives on a TV show and to "get a life".

"I didn't want anything to do with a group of obsessives who paid to get together to talk incessantly about a TV show that had been canceled. It wasn't logical," he wrote in an article for British national newspaper Daily Mail in 2008.

But on Friday the Canadian-born actor appeared moved by the masses of fans who have undertaken the pilgrimage to celebrate Star Trek, the series that has turned him into one of the most-loved actors on the small and big screen.

"I've never been ambivalent. I'm only filled with gratitude with the fame it gave me years ago and the way it's kept me in the public eye."

"I'm here at a large, huge convention in London, England, taking me from my home in Los Angeles all these years later and here you are, Reuters, talking to me and I'm very happy to be doing so."

In fact, Star Trek conventions have become an inspiration for the actor, who went behind the lens to film the 2012 documentary "Get a life!", examining what drives people to attend conventions.

"The conclusion that I come to is that it's (Star Trek) mythological. It's a desire for mythology that we don't have in this age."

That documentary followed 2011's "The Captains", in which he visits the other ex-Star Trek captains including Patrick Stewart, who played Captain Jean-Luc Picard in "Star Trek: The Next Generation", to probe their lives and careers with and without the sci-fi drama.

"In The Captains documentary, I examined the actors to find out what similarities we have, what drives ambitions, and talents and what differences. It made for an interesting and award-winning documentary."

The three-day London convention lasts until Sunday and is the first Star Trek live event to unite all five captains.

"I think it could be argued that we are all here today, the five captains, as a result of documentary."

Looking back at the start of the 46-year old series, which was canceled after the first three seasons before it started attracting a loyal following through re-runs, Shatner has embraced his Star Trek past.

"I had a great time doing it. I thought when it finished, that is the end of it. It wasn't. And it's all part of a magnificent journey."

(Editing by Paul Casciato)

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