There are plenty of great options: Giggs, Scholes, Baresi, Maldini, Facchetti, Puyol, etc.
For me though, the greatest is Francesco Totti. The others above played for clubs who won multiple trophies, and all won the champions league at least once. Aside from a smattering of Coppa Italias and one Scudetto, Totti didn’t win anything with Rome.
For me, it’s easier for a top player to stay at a top club, rather than be a top player like Totti and stay at a club that was rarely considered the best in Serie A. For my money, he is the greatest one-club man of all time.
Who would you choose?
Wild that nobody mentions Marco Reus. World cup winner who had more than enough quality to play in most top clubs back in the day, and yet stayed in a club that other than that one time never even showed signs of being competitive in the Champions League, and while playing in a league that was dominated by Bayern.
He neither won the world cup, nor is a one club man. He had almost 100 appearances at Gladbach.
Oh yeah, he got injured right before. I forgot. Still, he’s had every opportunity to leave Dortmund to be successful at a bigger club. He stayed loyal to his childhood club and he’s probably retiring there. Sure, he’s technically not a one club man, but for all effects and purposes he is. Not really worth arguing about this