A person cannot change who he is, especially if he has a bad character, no matter how hard he tries.
The waiter tried to be friendly to his customers but a leopard can’t change its spots and he was still very rude.
This idiom comes from the Old Testament (Jer. 13:23). The Hebrew prophet Jeremiah tries to persuade an evil shepherdess to become good but when he realises that it is impossible to convince her, he says: “Can the Ethiopian change his skin, or the leopard his spots?”
Some Christian commentators have interpreted this to mean that hard-core sinners cannot become good and will not be saved by God; they are doomed to be punished. Others have suggested that, while it’s very difficult for a long-standing sinner to change and be saved, it’s not impossible.
Other Idiomatic Expressions with the same meaning
The tiger cannot change its stripes
Un leopard ne peut pas changer ses taches
Correct French idiom
Chassez le naturel, il revient au galop