2015 has been the year of the revenge bod, gym selfie and beauty experiments! That meant there were plenty of Hollywood transformations over the past 12 months, but these 13 stars truly rocked both red carpets and Instagram feeds alike.

1. Caitlyn Jenner

No one made a bigger transformation this year than Caitlyn Jenner. After announcing that she was a transgender woman in an eye-opening, endearing 20/20 interview with Diane Sawyer in April, the 66-year-old former Olympian said goodbye to Bruce and made her debut as Caitlyn on the July cover of Vanity Fair. She then continued to tell her story of adjusting to her new life as a woman through her docu-series, I Am Cait.

2. Khloe Kardashian

Hello, revenge bod! Following her initial split from husband Lamar Odom, Caitlyn's stepdaughter had one of the most impressive body transformations this year, and she hasn't been afraid to flaunt the results of her 35-pound weight loss. The 31-year-old Keeping Up With the Kardashians star not only documented her weight loss for fans, posting workout shots galore on Instagram, but she also revealed her toned bod on the covers of Complexand her own book, Strong Looks Better Naked.

3. Melissa McCarthy

The Mike & Molly star hasn't been shy about her struggles with self-image and weight issues.

Last year, she admitted to People that in her 20s, she "used to cry about why I wasn't thinner or prettier." At the time, the 45-year-old comedy queen also said that she "never felt like I needed to change," but by this summer, she had dropped an estimated 50 pounds. "I finally said, 'Oh, for God sakes, stop worrying about it,' and it may be the best thing I've ever done," she admitted on CBS This Morning in June. The mom of two looked svelte and fabulous, which was especially evident as she promoted her new clothing line, Melissa McCarthy Seven7.

4. Jared Leto

The 44-year-old actor doesn't shy away from challenging roles, even if that means transforming his entire body and chopping off his long, lustrous locks to play the part.

Even though we learned that during the weight-loss rollercoaster he went on to play the part of Rayon in 2013's Dallas Buyers Club, our jaws still dropped in April when we saw the first photo of Jared as The Joker in Suicide Squad. The 30 Seconds to Mars frontman was barely recognizable thanks to a shock of neon green hair, head-to-toe tattoos and disturbingly dirty teeth. Apparently inspired by the bold hue, Jared debuted pink strands at the 2015 MTV Video Music Awards in August, a shade he's still rocking.

5. John Goodman

He's come a long way from his Roseanne days! The acclaimed actor hit the red carpet in October for the premiere of Trumbo looking nearly half his size -- especially noticeable if you saw his much fuller figure in that very flick.

John's weight has fluctuated over the years -- the 63-year-old also dropped 100 pounds back in 2010. That same year, he revealed to David Letterman that he had once ballooned up to 400 pounds.

6. Kylie Jenner

After much speculation about her plump pout, Kylie finally admitted that she uses lip fillers. "It's just an insecurity of mine," she revealed on a May episode of KUWTK. But the youngest member of the Kardashian-Jenner clan -- who still denies having any plastic surgery done -- hardly left experimentations to just injections. The makeup maven turned 18 this year, and with adulthood came a dizzying array of jaw-dropping, cleavage-baring outfits and wigs, most of which were documented on Snapchat.

7. Kevin Smith

His new bod was seven years in the making! In June, the 45-year-old filmmaker tweeted side-by-side photos on Twitter, showing himself with his daughter, Harley Quinn, in 2008 and again seven years later. The New Jersey native revealed he had dropped an impressive 85 pounds while joking about his informal attire. "I shan't wear pants and will never abort the shorts," he wrote.

8. Abby Lee Miller

The Dance Mom star went from a size 24 to 16, but she didn't shed the pounds on purpose. The 49-year-old reality star lost weight due to a prescription medication she was on for a thyroid condition.

When she got the drug refilled in Australia, she discovered that the pills weren't coated like they are in the U.S., which caused her to be sick for nearly a month. Though accidental, Abby Lee told ET in June that she's embracing her smaller size by watching her weight, which was down at least 18 pounds. "I haven't kept a record or thought about it or been on a scale," she said. "Let me say this: I've always had to go to a plus-sized store, and now I don't."

9. Liam Neeson

Fans were worried when paparazzi photos of the 63-year-old actor surfaced over the summer, revealing a frighteningly frail frame.

Turns out that much like Jared, this change came for a movie role -- Liam lost 20 pounds for Martin Scorsese's new film, Silence. "Martin wanted us all to look a bit more gaunt, which [stars Adam Driver and Andrew Garfield] did as well," Liam explained to press at the 4th Annual Los Cabos International Film Festival in November, where he looked noticeably healthier.

10. Kim Kardashian

The entire Kardashian clan seems to have updated their looks in one way or another in 2015, and Kim was no exception. Back in March, the 35-year-old mom of two -- she gave birth to son Saint West on Dec. 5 -- debuted platinum strands just in time for Fashion Week. But much like the lighter looks she's flirted with in the past, this one was also short-lived, lasting a mere 21 days.

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