The teenager moved to the energy drinks firm's premier team before May's Spanish Grand Prix in May - a race he ultimately won.
It was only Verstappen's second year in Formula One, and only his second season in car racing altogether, but he's already been marked as a future legend.
"He has done an enormously impressive job," Horner said of Verstappen’s season. "To have jumped in the car and won his first Grand Prix and then go on to finish on the numerous podiums that he has achieved.
"He has had stand out drives, not only Barcelona, he was very strong in Montreal, he drove brilliantly in the wet in Silverstone, he was very strong in Austria, he drove a great Grand Prix in Japan, very strong in Mexico."
"Brazil was an absolutely outstanding drive," Horner added. "And he produced another great drive in Abu Dhabi. He has marked himself out as a man of the future."
Bahrain International Circuit - Winter testing