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?
From a Scottish point of view maybe John Greig
John Greig CBE[5] (born 11 September 1942) is a Scottish former professional footballer who played as a defender. He spent his entire career with Rangers, as a player, manager and director. Greig was voted “The Greatest Ever Ranger” in 1999 by the club’s supporters,[6] and has been elected to Rangers’ Hall of Fame.
To be manager and director as well, giving your whole career to the same club. Very impressive