Men's soccer: Cristiano Ronaldo
Real Madrid forward
Age: 30
Ronaldo took home the Ballon D'or in 2014 and carried Portugal to the World Cup despite being knocked out in the first round. He has 18 goals in 2015 and 50 goals in 47 games for the 2014-15 season.
Women's soccer: Nadine Kessler
German national team midfielder
Age: 27
Kessler won 2014 FIFA's women's player of the year and leads a German team that's one of the favorites going into the 2015 Women's World Cup.
Men's tennis: Novak Djokovic
Women's tennis: Serena Williams
American tennis player
Age: 33
Williams won seven titles in 2014, including the US Open, and is 20-0 in the 2015 season. Her own inconsistency is her biggest problem, but when she's healthy and focused, she's unbeatable.
next slide will load in 15 secondsSkip AdSkip AdMen's basketball: LeBron James
Cleveland Cavaliers forward
Age: 30
LeBron James has a rightful case for MVP each season. The Cavaliers won 20 more games with James this year while the Miami Heat lost 17 more games without him. All the while he puts up monster stats every night.
Women's basketball: Maya Moore
Minnesota Lynx guard
Age: 25
Moore won the 2014 MVP award, averaging 24 points and 8 rebounds per game, and then led USA Women's Basketball to gold in the 2014 FIBA World Cup while winning player of the tournament.
Football: J.J. Watt
Houston Texans defensive end
Age: 26
Watt is the reigning NFL defensive player of the year and the runner-up for MVP. He had 20.5 sacks on the year, one interception, and even had three receiving touchdowns on offense. He's almost uncontainable for offensive lines.
Men's track and field: Usain Bolt
Jamaican sprinter
Age: 28
Bolt doesn't compete often outside of the Olympics, but when he does, he dominates. He set the world records for 100m and 200m at the 2012 Olympics. He recently ran his slowest 100m time ever, and still won the race.
Women's track and field: Genzebe Dibaba
Ethiopian middle- and long-distance runner
Age: 24
Dibaba was named 2014 sportswoman of the year for setting indoor world records for 1500m, 3000m, and a two-mile. She ran the second-fastest 5K ever in March, missing the world record by two seconds.
next slide will load in 15 secondsSkip AdSkip AdMen's skiing: Marcel Hirscher
Austrian skier
Age: 26
Hirschel has been the men's No. 1 ranked skier for four years. He's the first skier to win four straight World Cup titles, and he needs just two more to have the most titles overall.
Women's skiing: Tina Maze
Slovenian skier
Age: 31
Maze took home three medals at the 2015 World Ski Championships, including a gold medal in the combined event — an event that's "designed to determine the best all-around skier." She was nominated for Laureus Sportswoman of the Year in 2015.
Women's MMA: Ronda Rousey
UFC fighter
Age: 28
Rousey typifies dominance. She's 11-0 in MMA and 5-0 UFC fights. Her last two fights have lasted an average of 15 seconds.
Men's swimming: Chad le Clos
South African swimmer
Age: 23
Le Clos was named FINA World Swimmer of the Year in 2014 after he dominated the 2014 World Championships, winning gold in the 50m, 100m, and 200m butterfly, as well as the 200m freestyle. He also won two gold medals in the 2014 Commonwealth Games, one for the 400m medley.
next slide will load in 15 secondsSkip AdSkip AdWomen's swimming: Katie Ledecky
American swimmer
Age: 19
Ledecky is a three-time All-Met Girl's Swimmer of the Year and currently owns the world records in the 400m, 800m, and 1500m freestyle. She could become the first woman to win four individual gold medals at a single World Championship this August.
Baseball: Clayton Kershaw
Los Angeles Dodgers pitcher
Age: 27
Kershaw had one of the best pitching seasons in MLB history on his way to winning the 2014 Cy Young. He led MLB in wins, ERA, WHIP, and was second in opposing batting average.
Men's cricket: Mitchell Starc
Australian cricketer
Age: 24
Starc helped lead Australia to win the 2015 World Cup and was named Player of the Tournament in the process. He led the entire tournament with 22 wickets.
Women's cricket: Sarah Taylor
English cricketer
Age: 25
Taylor was the T20I Women's Cricketer of the Year in 2013, and during a stint playing in Australia in 2014 was named the South Australian Scorpions Player of the Year for 2014-2015.
Hockey: Alex Ovechkin
Washington Capitals
Age: 29
Ovechkin was first in goals in 2014-15, scoring 53 — his most since 2009 — and had 81 points, the fourth-best in the NHL and his most since 2010.
next slide will load in 15 secondsSkip AdSkip AdMen's squash: Mohamed Elshorbagy
Egyptian squash player
Age: 24
Elshorbagy is the No. 1 ranked squash player in the world. He won five events in 2014, including the World Series tournaments in Hong Kong and the US Open.
Women's squash: Nicol David
Malaysian squash player
Age: 31
David has been the world's No. 1 ranked women's squash player for eight years running and is often considered the greatest women's squash player ever. In 2014, she won a record-setting third straight US Open title.
Men's golf: Rory McIlroy
Irish golfer
Age: 25
McIlroy didn't win The Masters as he was expected to, but he did finish in fourth place with -12, his best finish ever. He needs one Masters win to become the sixth player to ever accomplish a career grand slam.
Women's golf: Lydia Ko
New Zealand golfer
Age: 17
Ko became the youngest No. 1 ranked player in professional golf in 2015. In 2014 she won three LPGA tournaments and has already won the Women's Australian Open in 2015.
Men's cycling: Alexander Kristoff
Norwegian road cyclist
Age: 27
Kristoff has steadily improved since becoming pro in 2010. He had 14 victories in 2014, including two stage victories in the Tour de France, and he has 11 victories already in 2015.
next slide will load in 15 secondsSkip AdSkip AdWomen's cycling: Pauline Ferrand-Prévot
Men's figure skating: Yuzuru Hanyu
Japanese figure skater
Age: 20
In 2014 Hanyu took first place for the second straight time at the Japanese Figure Skating Championships, won a gold medal at the 2014 Olympics, and won the 2014 World Championships in Japan. In 2015 he's already won his third straight national Japanese title and recovered from an injury to finish second at the World Figure Skating Championships.
Women's figure skating: Elizaveta Tuktamysheva
Russian figure skater
Age: 18
After a poor showing at the 2014 Olympics, Tuktamysheva has already won the Grand Prix Final, the 2015 European Championships, and dominated the 2015 World Championships, winning by nearly 17 points.
Auto racing: Lewis Hamilton
British Formula 1 driver
Age: 30
Hamilton won his second season title in 2014, and already has three first-place finishes and a second-place finish in 2015.
Men's gymnastics: Kohei Uchimura
Japan
Age: 26
Uchimura is often considered the greatest gymnast of all time. He's won five Olympics medals and 16 World medals. In 2014 he became the first gymnast to win five consecutive World all-around titles.
next slide will load in 15 secondsSkip AdSkip AdWomen's gymnastics: Simone Biles
American gymnast
Age: 18
Biles is set to dominate her first Olympics in 2016. She won four gold medals at the 2014 World Championships and took first place at the 2015 AT&T American Cup.
Men's rugby: Richie McCaw
New Zealand rugby player
Age: 34
McCaw is the captain of the All Blacks, New Zealand's national rugby team, which won the 2011 World Cup and the 2014 World Rugby Team of the Year. McCaw has won World Rugby Player of the Year three times and has been nominated five other times.
Check out our collection of dominant athletes across the world