Who is Jonathon Simmons, the Spurs' sorta secret weapon?

After everyone picked up their jaws from the floor following the San Antonio Spurs' season-opening beatdown of the Golden State Warriors, the most popular non-Warriors question on people's minds was this:

Who was that Jonathon Simmons kid?

Simmons, thrust into the lineup thanks to Danny Green's injury, was a man on fire. He flew through the air for a chasedown block of Steph Curry and posterized poor JaVale McGee with a dunk.

He shot threes (3 of 5) better than Curry (3 of 10) and scored a career-high 20 points in 28 minutes. He took 14 shots — third-most on the team (and more than Klay Thompson took).

Oh, and he played defense —  the biggest key to earning Coach Pop's trust and cracking the lineup.

OK, really, who was that guy?

The 27-year-old swingman played in 55 games as a rookie last season, averaging six points in almost 15 minutes per game, but just three games in the playoffs, as his playing time was cut in half. So if you didn't pay close attention to the Spurs during the regular season — and who did, with the Warriors and Cavs stealing all the headlines? —€” then you might've missed moments like his 19-point game against Dallas in the finale, or an 18-point performance at Milwaukee, where the fans chanted "Who are you?"

The answer is he's the biggest Cinderella in the NBA, with a journey that's been called "the greatest story in basketball".

Simmons played one season at the University of Houston before declaring for the draft in 2012. He went undrafted, however, and ended up first in the ABL, then the D-League for two seasons. A father of four daughters, Simmons considered giving it all up.

"I bought him lunch a couple times last year, because he didn't have money to eat," Phoenix Suns coach Earl Watson, one of Simmons' coaches in the D-League, told the San Antonio Express-News. "I had to help him buy shoes, because he didn't have any shoes."

Simmons played in the summer league last year and impressed the Spurs, who signed him, but his journey was far from over. He was assigned back to his old D-League team by the Spurs and recalled twice at the start of last season, and again in March. This past summer he played in the summer league again.

In short, Jonathon Simmons is a grinder proving himself again and again and again. Now he's doing it at the highest level against the best in the business.

"I think it's been very important in the sense that he was down there for a while and never lost hope," Spurs coach Gregg Popovich told the Express-News of Simmons' time in the D-League. "He basically paid his dues."