It was a guy dressed up as Theodore Roosevelt, since been nicknamed "Teddy Goalsevelt."
His incredibly inspirational mustachioed scream gave hope to Americans all over the world watching the game.
People have been tweeting nonstop about him since.
And the fans who have internet down in Brazil have been sharing photos of the 26th president walking around. But the question remains, who is this man?
Thankfully, the folks over at Yahoo! Sports tracked him down. His name is Mike D'Amico and he actually wasn't aware he had become an internet sensation.
D'Amico told Yahoo he decided to wear the costume because he thought people would be more likely to sing-a-long to USA chants if Teddy Roosevelt were leading them.
But he definitely doesn't mind the newfound fame.
Go get 'em, Mr. President.
In real life, Teddy Goalsevelt (Mike D’Amico) is an associate creative director at Cavalry, the lead ad agency for Coors Light. Cavalry are now raising money to keep D'Amico down in Brazil for the whole World Cup. The agency promised to match every dollar donated up to $2,500.