"Knowing that the best in the world chose Juventus, knowing that the team that I consider the best in the world finally signed the best player in the world - it's a huge honour," said Agnelli.
"I have always thought, and I will always think, that the team makes all the difference in any company, but having the best professionals in each position helps achieve the best results," he added.
The Juventus president carried out the most expensive transfer in Italian football history when he signed Ronaldo in the summer from Real Madrid for €112m.
Agnelli, who has presided over a hugely successful period at Juventus, with seven consecutives league titles, showed his conviction that Ronaldo would help bring the Old Lady the Champions League trophy, not seen in Turin since 1996.
"Cristiano will undoubtedly help us obtain our objectives, although we have to remember to take things one game at a time - the results we get in October will help us when it comes to May," he said.
Juventus are currently top of Serie A, four points ahead of Napoli in second, and they are also top of their Champions League group with maximum points from their first three games.