Gyokeres' former team-mates and coaches remember a young boy who cried when he lost. They talk about a "stubborn kid" who was "wild, really aggressive" and would occasionally come to blows with team-mates.
"I remember the older players were sometimes telling him to calm down a little bit, because he was always going all-in," Magni Fannberg, who handed Gyokeres his first-team debut for Swedish club Brommapojkarna in 2015, told the Times., external
There are stories about Gyokeres' single-mindedness, focus and drive.
Gustav Sandberg Magnusson, who played with Gyokeres at Brommapojkarna, adds: "There was one training session I was screaming at him, 'Viktor, pass the ball. Pass'. And he didn't [look at] me. I was so frustrated."
David Eklund, academy scout at the club, tells BBC Sport: "He was never a superstar like Dejan Kulusevski [another Brommapojkarna youth product]. But he scored goals. That's it.
"He had a strong mentality but he's a really nice guy. He always worked hard and had the idea of being a top player, training every day. He wanted to prove people wrong."
Dennis Lawrence, who was part of Mark Robins' backroom staff at Coventry when Gyokeres was there, says: "I had to laugh the other day when I saw he scored a free-kick for Sporting. At Coventry, he would try free-kicks [in training] and I would say, 'No, you're not on free-kicks, Viktor'.
"But his mentality is, 'no, I know I can do this.'
"And he's scoring these incredible free-kicks now. He's got that ability to focus on and achieve anything he wants."
It all started on the gravel pitches of his local grassroots club in Stockholm, IFK Aspudden-Tellus. Gyokeres was five at the time and he credits his father, Stefan, in his development.
"Making that journey together helped me a lot. We'd share good and bad moments," says Gyokeres, who has since gone on to make a big impression - on and off the pitch.
Recently he was the cover star for Vogue Scandinavia, who described the player as Swedish football's "pride and glory".