Carl Hester believes Great Britain's team dressage gold will give participation in the sport a major boost.
Laura Bechtolsheimer, Hester and Charlotte Dujardin held off the Germans to win at Greenwich Park.
It follows Great Britain winning a first showjumping gold medal in 60 years on Monday.
"It's shot our sport into a different league. We've had so many years of dreaming about it," Hester said.
"This is my fourth Olympics and it's weird because I've gone to three with no expectations and it's easy to ride like that.
"To come to an Olympics where we were possibly expected to get gold, gave me a frightening feeling, but this is a truly special moment for everyone involved in British dressage."
After Hester, 45, scored an Olympic record for his stage of the event with an 80.571 on Uthopia, Bechtolsheimer and Alf produced 77.794, leaving Dujardin facing the key test.
The 27-year-old and Valegro scored 83.286 to end any German hopes.
Hester paid tribute to Bechtolsheimer and Dujardin, who only took the sport up in 2007.
He added: "Those girls are cool customers and Charlotte is unbelievable for the amount of time she's been riding.
"The horse is also unbelievable, you can see he's the best horse in the world. We've finally won it and I said to Charlotte on the way here, I have a little saying for her, that, 'Some people wish it will happen, some people think it will happen and you are going to make it happen'.
"That's the sort of thing I can say to her. It would frighten a lot of people but she just takes it, goes in there, and rips through her test like a professional of 20 years would."