Peter Lindbergh/Allure

With fans and critics maintaining a watchful eye on what they're wearing, today's celebrities have become icons in the fashion world. From Lady Gaga's campy costumes to Rihanna's rebel chic edge, celebs hold a massive influence on consumer style trends.

Fittingly, many stars have traded in their claim to fame for lucrative careers in the fashion industry. Twins Mary-Kate and Ashley Olsen are among the most successful of this bunch, leaving the film industry 10 years ago to focus on their fashion empire. The twins appear on the cover of the December issue of Allure magazine (on stands Nov. 19) and in a candid interview, the child stars dish on their move to high fashion.

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"I was reading scripts, and ultimately I just said to the people who were representing me, 'I need to do things 100 percent. I don't feel like I can give you 100 percent of my time,'" Ashley explained of her decision to quit acting. "There's a lot of compromise in the entertainment industry. I can't sit in this room and audition for this part."

Mary-Kate continues to act regularly, but shares her sister's passion for expanding their brand. Together, the duo has three fashion brands: Olsenboyle for JCPenny, ready-to-wear Elizabeth and James, and high-end line The Row.

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To critics who question the twins' business ventures, the 27-year-old beauty had this to say: "It's such an uneducated perspective! You still have to grow within business. You have to take a chance."

Mary-Kate and Ashley are not the only stars to take their talents to the fashion industry. Take a look at four other celebrities turned designers below.

Nicole Richie:

Celebrity socialite Nicole Richie has come a long way from the short-lived reality series "The Simple Life." Shortly after the show wrapped, Richie launched a jewelry collection called House of Harlow 1960 in 2009. Later that year, she launched a second brand, ready-to-wear clothing line called Winter Kate. Together, the brands offers a full-fledged collection of clothing, footwear and accessories.

"I feel truly blessed to do what I love for a living," Richie said in an interview with the Telegraph in June. "I had no formal training, but designing was something I always gravitated to. When I was little, I used to be a competitive figure skater, and I used to design my own costumes with my father's costume designer."

"I have a very good team that I work with now, but I design everything myself," she added. "This is not something that I just put my name to."

Gwen Stefani:

"No Doubt" frontrunner Gwen Stefani has also enjoyed success in fashion with the Asian- and South-American-inspired line L.A.M.B.

"For me the line is genuinely for myself," she told CNN in 2011. "I want to make a line of clothes that I want to wear - it's kind of selfish…. I'm not going to ever be a Vivienne Westwood. I'm trying to make clothes to wear everyday, that's what LAMB is. It's not a couture line."

While Stefani has yet to abandon her career in music, the singer revealed she started L.A.M.B. as a viable alternative to retirement.

"I started the line honestly because nine or 10 years ago I didn't know how long I would be doing music," she explained. "They ask you, 'What are you going to do in 10 years?' and I didn't know. I just thought, by then I want to have a family and I'm not going to be doing music but I wanted to do something creative."

Victoria Beckham:

Spice Girl Victoria Beckham is bringing a posh edge to the fashion industry with her self-titled ready-to-wear clothing line. The Victoria Beckham Collection won Designer Brand of the Year at the 2011 British Fashion Awards and the British beauty has big plans for brand's future.

"I want to get bigger and bigger," she said in an interview with the New York Times' T magazine this summer. "I absolutely want an empire."

"I want to reach as many women throughout the world as I can," she continued. "There are more categories that I want to enter into. I have five categories at the moment. But at some point I would love to do shoes, I would love to do fragrance, I would love to do makeup, I would like to do underwear. There are so many things I want to do."

Jessica Simpson:

"Irresistible" singer Jessica Simpson launched her self-titled fashion line in 2006 as a shoe collaboration with footwear designer Vince Camuto. Since then, the Jessica Simpson Collection has expanded to include a wide range of merchandise including clothing, footwear, accessories and fragrances.

"I want everyone to be able to wear my designs," Simpson told People magazine in February. "The collection is accessible - from extra-small to plus and maternity, there is something for everyone to feel great in."