Michael Greller made a bold decision in 2013, walking away from the steady paycheck of his teaching career, choosing to chase down a dream by caddying for Jordan Spieth, then the top-ranked amateur golfer in the United States. With the 2015 PGA Tour season now complete, it seems like that gamble paid off: Greller likely earned about $2 million this year caddying for Spieth, now the top-ranked professional golfer in the world.

Caddies typically get paid on a system of performance-based tipping, Golf Digest said. The common system allows for caddies to take home 5 percent of a golfer's winnings for a made cut, 7 percent for a top 10 finish and 10 percent for a win. Using that system Business Insider calculated Greller's haul for the year to be around $2.1 million. That is a higher winnings figure than 211 PGA Tour golfers. Tiger Woods, for instance, earned just $448,598 on the course this season. Golf Digest estimated Greller could have pulled in even more, pegging his total as high as $2,225,613.

Spieth Greller PGA Jordan Spieth celebrates with his caddie Michael Greller on the 9th green during the second round of the 2015 PGA Championship golf tournament at Whistling Straits, Aug. 14, 2015. Photo: Reuters

That total, which doesn't include a weekly stipend golfers typically pay to caddies, is so large because Spieth won five times on tour, including two majors and the Tour Championship last weekend. The 22-year-old also finished in the top 10 an eye-popping 15 times and won the FedEx Cup playoffs, which comes with a $10 million bonus that likely paid Greller $1 million.

Greller first met Spieth in 2011 when the then-schoolteacher caddied for the Texan at the 2011 U.S. Junior Amateur at Gold Mountain in Washington state. Spieth won the tournament and would go on to bring Greller back on board when the golfer played in the 2012 U.S. Open. From there, Greller quit his job to caddy full time for Spieth. But the 37-year-old's lessons from his time as a teacher apparently have carried over to the golf course.

“Everything I have done in my life prepared me for this, specifically teaching for 10 years,” he told the Seattle Times in 2014. “Being able to think on your feet, being adaptable and having thick skin. … You are going to mess up -- and if you are not confident in yourself, your player picks up on that. You have to be willing to serve and encourage. Just like in teaching.”

Spieth Greller Augusta Jordan Spieth of the hugs his caddie Michael Greller after winning the Masters golf tournament at the Augusta National Golf Course in Augusta, Georgia, April 12, 2015. Photo: Reuters

Since then, Greller and Spieth have developed a comfortable relationship while the former teacher is making huge paychecks doing a job he used to perform for free. In the eyes of Spieth and Greller, they have a familial of relationship and often are seen embracing on the course.

“Every day, someone asks if we were teammates or classmates. I always tell him it’s because of his receding hairline. I get a kick out of that,” Greller told GolfChannel.com in 2014. “I see it more as a brotherly relationship. We compete hard and talk a lot of trash. I was born and raised in Michigan. He picks on my teams; I rag on his Texas teams.”

After the season the two experienced in 2015, with wins at the Masters and the U.S. Open, there's likely a lot less time for ragging in between all of the celebrating.