Everyone knows those guys at the gym, half-heartedly lifting weights while checking their phone in between sets, downing a protein shake afterwards, talking about how they should be competing. Most people can build up a fair amount of muscle mass if they put in a bit of effort. However, there’s a big difference between the casual gym goer and bodybuilders.

Simply put, bodybuilders generally train a lot more than the average guy. After all, they’ve decided that their body and physique will be their tool, their career. It only makes sense that they’d spend countless hours in the gym honing their physique. While all that effort certainly makes an impact, at the end of the day, many of the biggest bodybuilders are also absolute genetic freaks. They have an incredible capacity to pack on muscle and, over the years, just managed to grow bigger and bigger.

The bodybuilders on this list come from all over the world, Europe to the U.S., and have varied backgrounds. While some got their start almost as children, picking up their first weight at 11 or 12 years old, others were late bloomers who only got into fitness when they reached 19 or 20. Regardless of how they started training, who they trained with, and whether they took hiatuses in their career or have been stable staples on the competition circuit, the bodybuilders on this list have all risen to the top of their game and made a huge impact in the fitness world.

They’ve done everything from acting to consulting as side projects, and have set countless records over the years. They’re the kind of guys who would be incredibly intimidating to run into in a dark alley, even though they’re pretty much all gentle giants who love their families. They’re lean, mean training machines, and their physiques are absolutely mindblowing.

Here are 15 of the biggest bodybuilders of all time.

15 15. Kevin Levrone

Levrone first got into bodybuilding at the young age of 11, because his older brothers were lifting. He lifted alongside them and found out that he was pretty good at it. He started to do some research, learning about the big bodybuilders in the 1980s such as Lee Haney and Arnold Schwarzenegger. His first pro qualifying event was the 1992 Chicago Pro Invitational, and he was soon setting the bodybuilding world afire. While he’s never garnered the coveted Mr. Olympia, he’s come in the top 5 countless times. Levrone is now in his late 40s and hasn’t competed for about a decade – instead, he’s trying to break into acting. But who knows – the Maryland Muscle Machine might make a comeback some year.

14 14. Lou Ferrigno

Come on – no list of the biggest bodybuilders would be complete without the Incredible Hulk. Lou Ferrigno had a difficult childhood, as his hearing loss (which came from an ear infection in his youth) led him to be very shy. He was a gangly youth, reading comic books and dreaming of being as strong as the muscular characters within – and he certainly attained that goal. He first picked up a weight when he was 12, and trained enough over the following decade that he officially became the youngest man to win the IFBB Mr. Universe competition twice. He was also the tallest to have done so, and the only one to have gotten two consecutive wins. He was also among the youngest to enter the prestigious Mr. Olympia contest, strutting on the stage at 23 years of age. He eventually realized his childhood dream by becoming The Incredible Hulk and entering the world of Hollywood.

13 13. Dennis Wolf

Wolf was born in the former USSR but eventually moved to Germany with his family at the age of 14. Like many of the bodybuilders on this list, Wolf got his start fairly young, at the age of 15. His interest was peaked by a bodybuilder magazine that his father bought him, and he soon started getting in shape and was competing at 21. He turned pro in 2005, and made his IFBB professional debut in 2006. He shows no signs of slowing down (or getting any smaller) as he continues to work on his physique. He’s built up an incredibly impressive size, and one thing’s for sure – whatever this Big Bad Wolf wants, he probably gets.

12 12. Moustafa Ismail

Even those who don’t know much about bodybuilding likely recognize Moustafa Ismail – he got a lot of attention recently for initially setting a Guinness world record for the biggest arms, biceps and triceps, and then sparking some controversy regarding whether his accomplishments were all natural. His 31 inch guns are astounding and he claims to be able to lift 600 pounds. While many have accused him of steroid use, Ismail continues to assert that his muscles are the result of a diet that is very heavy in protein (his daily diet apparently contains four pounds of chicken and two pounds of steak every day). The Egyptian bodybuilder (who moved to the US in 2007) also works out for three hours a day to keep his physique up.

11 11. Lee Haney

The Mr. Olympia is one of the biggest, most prestigious competitions in the world of bodybuilding, and most bodybuilders dream of earning the coveted title at least once in their career. Haney has won it eight times, consecutively – a record that even one-ups the infamous Arnold Schwarzenegger’s seven-title streak. Haney dominated the bodybuilding world in the 1980s and has since retired into a much quieter life. Haney lives with his wife and two children in Georgia, and owns two fitness centers in Atlanta. While he works with and helps train athletes, putting his years of bodybuilding knowledge to good use, he also founded a non-profit retreat facility for children, putting his degree in youth counseling to good use.

10 10. Johnnie O. Jackson

Johnnie O. Jackson is a beast, plain and simple. Though standing only 5’8 in height, this American bodybuilder has deadlifted a record-setting deadlift of 760 pounds. He can also bench press 600 pounds, but that seems like child’s play compared to his deadlift record. When he’s not on stage, Jackson works as a personal trainer, helping other individuals work towards a physique half as impressive as his. Before he stepped into the public eye as a beloved bodybuilder, he even served in the armed forces, something that Jackson says helped shape his life philosophy and build his discipline.

9 9. Flex Wheeler

This bodybuilder’s real name is Ken, but everyone knows him as “Flex” Wheeler – but one look at his body will tell you he doesn’t need to be flexing for his muscles to pop. Wheeler has been racking up the competition wins since 1993, and even got the coveted ‘triple crown’ in 1997 (which, in the world of bodybuilding, means wining the Ironman, Arnold Classic, and San Jose Classic). Sometimes referred to as “The Sultan of Symmetry,” his physique at the height of his competition years was flawless.

8 8. Roelly Winklaar

Roelly Winklaar is a bit of a newcomer in the world of bodybuilding – while many of the ‘greats’ hit their peak in the 1980s or early 1990s, Winklaar is just getting into the swing of things now. Winklaar manages to pack 285 pounds of pure muscle onto his small 5’6 frame. One of his first competitions was the 2009 NPC Arnold Amateur Championships, and he placed first right from the start. He’s only continued to excel from there, continually impressing bodybuilding fans with his incredible physique. Winklaar could very well be one of the next big names in bodybuilding, so keep your eye on his progress as he goes forth with his career.

7 7. Phillip Heath

Phillip Heath – who many know by his nickname, “The Gift” – grew up in Seattle, Washington, and was a typical high school jock. He played varsity basketball, and excelled enough that he earned a basketball scholarship to the University of Denver. He played as the point/shooting guard at the University’s Div 1-A basketball team. While he loved basketball, he was looking for his next challenge, and it was only after university that he found the world of bodybuilding in 2002. He pushed his body from 185 pounds to 215 pounds of pure muscle, before cutting down to 192 pounds for his first competition, The Rocky Mountain NPC USA Championship “Northern.” Heath won – quite the way to start out his career. He trained harder, got even bigger, and eventually racked up a whole slew of other titles, including his IFBB Pro card and four Mr. Olympia wins.

6 6. Kai Greene

American bodybuilder Kai Greene turned to weights as a way to cope with a difficult childhood, and his seventh grade English teacher helped introduce him to the world of competitive bodybuilding. He started out on the teen circuit, flexing his growing muscles, before taking a hiatus to really transform his physique. He turned pro before his 19th birthday, earning him the honor of being the youngest natural professional bodybuilder at the time. He continually improved himself, moving on to the NPC to qualify for recognition with the IFBB. Kai’s admirable determination paid off almost 16 years after he first entered the bodybuilding circuit when he became one of the buff athletes in the IFBB Professional ranks.

5 5. Gunter Schlierkamp

Not all famous European-born bodybuilders come from Austria – Gunter Schlierkamp, a retired German IFBB Pro, hails from Olfen, Germany. However, it was a certain Austrian muscle machine who inspired Schlierkamp – he saw Schwarzenegger in some of his films and was inspired to sculpt his own body. He started training at 16 and entered (and won!) his first competition at 18. He own the Mr. Universe title in 1993, and made the move to the U.S. in 1996 – just like Arnold! In addition to competing, Schlierkamp has done some acting, modeling, and frequently works with companies as a consultant in product development.

4 4. Arnold Schwarzenegger

Even if you know absolutely nothing about bodybuilding, chances are you know who Arnold Schwarzenegger is. The Austrian-born bodybuilder set records in the fitness world, becoming the youngest person to win the Mr. Universe title when he was 20. He racked up countless titles over the years, including four more Mr. Universe titles and seven coveted Mr. Olympia titles. After an illustrious career in bodybuilding, Schwarzenegger (who had become a U.S. citizen after emigrating to the U.S. in 1968) started conquering another industry – Hollwood. He had roles in several movies, including Hercules, Stay Hungry (for which he won a Golden Globe), and Conan the Barbarian. The film that absolutely made his career, however, was Terminator. With three simple words – “I’ll be back” – Schwarzenegger cemented his place as a pop culture icon.

3 3. Markus Ruhl

Unlike many bodybuilders on this list who picked up their first dumbbell at the ages of 12 or 14, Markus Ruhl, who is sometimes nicknamed “The German Nightmare,” got a bit of a late start. The then 140 pound German-born Ruhl started lifting at nineteen, and after five years, finally competed in his first competition – over 100 pounds heavier, at 243 pounds. He won the heavyweight and overall title at his first competition, the Bachgau Cup, and began a long career of bodybuilding. He soon received his pro card, continued packing on additional muscle mass, and simply grew and grew his amazing physique.

2 2. Dennis James

Though he’s an American, muscle man, Dennis James was born in Heidelberg, Germany, as his father, a military man, was stationed there. Perhaps it’s that German bodybuilding blood, but James began lifting at 18 and immediately started to impress everyone. James hasn’t had as many impressive finishes as some of the big bodybuilders – though he’s competed in the Mr. Olympia seven times, his best finish is fourth place. However, he’s consistently maintained his physique over the years, proving that you don’t always need titles to keep up your motivation.

1 1. Ronnie Coleman

Ronnie Coleman is an absolute beast, plain and simple. In a world where bodybuilders continue to grow bigger and bigger, Coleman has set a new standard – the Louisiana-born bodybuilder has a contest weight of about 300 pounds, something that not many bodybuilders achieve. Coleman got his start as a football player, initially working out so he could be more impressive on the field. He continued playing football while he attended Grambling State University, and actually planned to become an accountant. You heard it – this giant muscle man was planning to spend all his days at a desk. However, his plans changed when he moved to Texas for some new job opportunities. While doing everything possible to stay afloat in a hard job market, Coleman saw an advertisement for the police force, and started a career there. Coleman’s fellow officers convinced him to check out a particularly impressive gym in their neighbourhood, whose clientele consisted of powerlifters and competitive builders. The rest, as they say, is history. Coleman immediately impressed at his first competition in 1990 and soon began dominating the bodybuilding world, earning his IFBB Pro card as well as countless titles. In fact, Coleman holds the record for the most wins by an IFBB professional – a staggering 26, including eight coveted Mr. Olympia titles.