SAN DIEGO -- The wildly popular annual trade show Comic-Con International kicks off Thursday for a four-day run that will draw tens of thousands to downtown San Diego, including directors Steven Spielberg, Guillermo Del Toro and Jon Favreau.

This year's edition of what began as a modest comic book fair in 1970 and has since grown into a premier pop culture extravaganza comes despite a tumultuous off-season that almost led to the convention leaving San Diego. Both Los Angeles and Anaheim tried to lure Comic-Con away with promises of larger facilities and other incentives.

According to the San Diego Convention and Visitor's Bureau, the event has a total economic impact in the region of $162.8 million annually and generates $2.8 million in tax revenues. To prevent losing that, San Diego city officials offered to use $500,000 in hotel taxes to pay for Comic-Con shuttle service around downtown. They also offered to block out more hotel rooms for convention use and discount the rooms.

The move worked and in October, organizers announced the event would remain in San Diego until 2015.

This week's sold-out event is expected to draw around 126,000 people to downtown San Diego.

While Comic-Con has long been a major draw for top-notch actors, directors and other industry insiders to promote their latest work, this is the first time Spielberg will make an appearance. He is scheduled to appear Friday to discuss his forthcoming motion-capture release, "The Adventures of Tintin,'' based on one of the most popular European comics of the 20th century.

Another big-time draw is the cast of "Twilight.'' Die-hard fans began lining up on Wednesday to catch a preview of the latest film in the vampire-themed series.

Other highlights include Del Toro promoting "Don't Be Afraid of the Dark'' and "Pacific Rim;'' director Steven Soderbergh promoting "Haywire;'' director Francis Ford Coppola promoting "Twixt;'' and Favreau promoting "Cowboys & Aliens.''

Although Comic-Con has become a popular venue for large studios to promote their biggest, most expensive comic book-themed projects and other films that appeal to the fantasy-minded, more smaller films and big-name television series are squeezed into this year's line-up.

From TV, the casts of HBO's "Game of Thrones'' and "True Blood'' and AMC's "The Walking Dead'' will participate in panel discussions during the convention.

Another feature will be the DC Comics talent search in which DC Editorial Art Director Mark Chiarello will be available to look at aspiring artists' work.

Due to Comic-Con's popularity, city officials strongly suggest attendees use public transportation. The Metropolitan Transit System has beefed up its trolley schedule and is offering special four-day passes for $15.