On the outside, they all look the same: White armor, white helmets, black blaster rifles. Imperial soldiers from a galaxy far, far away, they're loyal only to the Empire and recognizable everywhere as "Star Wars" storm troopers. Inside, though, are different stories. Those armored clones are lovingly occupied by moms, dads, doctors, cops, lawyers, exterminators, artists and other passionate "Star Wars" fans who devote thousands of dollars and countless hours to building screen-accurate costumes and wearing them all over the world to support the beloved franchise as well as dozens of children's charities. They are the 501st Legion, an international, all-volunteer costuming group. And this week, they're coming to Comic-Con. "It's a major event for us every year," says Christi Ladnier, 42, a mother of three who will be wearing an eight-years-in-the-making homemade Boba Fett costume. (Legion members dress as all kinds of "Star Wars" characters, with storm troopers the most popular.) At least 200 members of the group — which boasts nearly 5,000 members in 40 countries — will be in full costume at the annual pop-culture festival, held Thursday through Sunday at the San Diego Convention Center. Comic-Con is just one of dozens of events Legion members attend each year. A major supporter of the Make-A-Wish Foundation, Legion members also lend their Imperial glory to children's hospitals, the Ronald McDonald House, the American Cancer Society, Toys for Tots, the Boys and Girls Clubs of America and March of Dimes. They've appeared in commercials, marched alongside "Star Wars" creator George Lucas in the Tournament of Roses parade and handed out Halloween candy at the White House. Charity is at the heart of the 501st Legion, and friendship and fandom are its soul, but it really comes down to the costumes. Their storm trooper outfits aren't store bought, nor are they cheap, and they must be identical to what's in the original films to be good enough. The Legion's standards division assesses the screen-accuracy of each member's attire. Storm trooper armor is made from vacuum-formed plastic, heated in home ovens and poured over molds meticulously sculpted based on careful analysis of the characters on screen. The artisans who make the outfits are Legion members themselves, and they sell their work for practically no profit under a unique agreement with Lucasfilm, owner of the "Star Wars" franchise. The company allows the fan group to use its intellectual property without fee or fine so long as the costumes, T-shirts and collectible coins that result are strictly for Legion members. "It's an extended family," says Steve Sansweet, Lucasfilm's director of content management, describing copyright concerns as "a non-issue" with the 501st Legion. Marcelo Gallo, 43, of Riverside, Calif., discovered hidden artistic talents when he decided to make his own storm trooper helmet. A married father of five and owner of a pest-control business, he spent his free time researching how to make molds and vacuum form plastic. Now he's built hundreds of helmets for fellow members and charity auctions. "Sometimes I wish I could do this every day, but I can't make it a top priority in my life because it's not a source of income," he says, adding that any money he makes goes back into the club and his costume. Mike Ozeroglu, 36, of Glendale, Calif., a radiation therapy physicist with the US Navy, ended up doing all the leatherwork on his Jengo Fett costume. "It's not something that you can just buy. You pretty much have to make it yourself," says, adding that refining the costume is a continuous process. "I've been working on that Jengo Fett literally since I first started in 2004." While he loves to "geek out on 'Star Wars' fandom," he says the real reward is bringing joy to sick kids. "The most fun is where we go off to the hospitals," he says. "The kids really think you're the character most of the time. It's fun to go in there and cheer them up a little bit. The following Monday I'm there as a staff officer and nobody knows I was there over the weekend." Though the helmets can get hot, they also help hide emotions and keep these costumed fans firmly in character, says Ladnier, who lives in Highland, Calif. "Sometimes you're glad you have a bucket on your head because you just start welling up." The costume itself also can be uncomfortable. Beneath the armor, which breaks down into some 60 pieces, members wear long-sleeved shirts and leggings, plus a swath of fabric around their necks. It takes around 20 minutes to get in costume. Wearers can be a bit clumsy, too, since the helmets obscure peripheral vision. But owning and wearing the storm trooper suit is the ultimate fan experience, says Los Angeles attorney Lawrence Green, who says he's "over 30." "Some people collect action figures," he says. "We get to BE action figures." Doing charity work began as an afterthought, says Legion founder Albin Johnson, but is now at the core of the group's activities. "We had to find things for people to do in armor," says the 41-year-old from Columbia, S.C. "And charity would validate us in a way that says, 'Hey, world, you can make fun of us as kind of goofy but we're justifying what we're doing by charity alone.'" A decade later, the Legion's charitable outreach extends both inside and outside the group. Members have donated kidneys to each other — twice. When Johnson's daughter was diagnosed with a brain tumor, Legion members cooked dinners for the family, cleaned their house and mowed their lawn. "These guys are literally giving parts of themselves to keep other 'Star Wars' fans alive and well," Sansweet says. "They're giving back to all fans by doing what they do and providing this sense of wonder and excitement." So what makes grown adults spend thousands of dollars and hundreds of hours to dress up like fictional characters from their favorite film? Ultimately, its camaraderie, says Johnson, and esprit de corps. "Every human being is a social animal, but a lot of sci-fi geeks aren't seen that way," he says. "It's successful because you've got a lot of people that say they had no way of celebrating 'Star Wars' fandom in a way that felt good until they had people to do it with, charities to do it for and events to do it at."