Answer by taking a quote from the following article:

Gennady Golovkin was born on April 8, 1982, in the city of Karaganda in the Kazakh SSR, Soviet Union (now Karagandy, Kazakhstan) to a Russian coal miner and Korean mother, who worked as an assistant in a chemical laboratory. He has three brothers, two elder named Sergey and Vadim and a twin, Max. Sergey and Vadim had encouraged Golovkin to start boxing when Golovkin was eight years old. As a youth, Golovkin would walk the streets with them, who went around picking fights for him with grown men.

On July 20, 2012 it was announced that Golovkin would defend his titles against European champion and The Ring's #10-rated middleweight Grzegorz Proksa (28-1, 21 KOs) on September 1 at the Turning Stone Casino in Verona, New York. The fight was televised on HBO in the United States and Sky Sports in the UK. Golovkin put on an impressive performance in his American debut by battering Proksa to a fifth-round TKO, which was Proksa's first loss by knockout. Proksa praised Golovkin's power, "The guy hits like a hammer. I tried everything, but it did not work. You have to give him credit, because he had a good handle on the situation and it was an honor to meet him in the ring." CompuBox Stats showed that Golovkin landed 101 of 301 punches thrown (34%) and Proksa landed 38 of his 217 thrown (18%).  In October, when the WBA (Super) middleweight champion Daniel Geale signed to fight Anthony Mundine in a rematch, the WBA stripped Geale of the title and named Golovkin the sole WBA champion at middleweight.  On November 30, 2012 it was announced that Golovkin would next fight The Ring's #9-rated light middleweight Gabriel Rosado (21-5, 13 KO) on the HBO Salido-Garcia card in the co-main event. on January 19, 2013. It was said that Golovkin would agree a catchweight of 158 pounds, two pounds below the middleweight limit. Rosado later rejected the proposal, stating he would fight at the full 160 pound limit.  Golovkin continued his stoppage-streak with a TKO victory over Rosado. The fight was halted when Rosado's corner threw in the towel to save Rosado, who was battered and bleeding heavily from his nose and left eye. At the time of the stoppage, Golovkin led on the judges' scorecards 60-54, 60-54, and 59-55. According to CompuBox Stats, Golovkin landed 208 of 492 punches thrown (42%) and Rosado landed only 76 of his 345 thrown (22%).

did golovkin hit hard?
Golovkin put on an impressive performance in his American debut by battering Proksa to a fifth-round TKO, which was Proksa's first loss by knockout.