Alexander the Great

[LwyrFirat]

As it is well known Alexander the Great is a famous military commander in history. However this name confuses me in terms of grammer, since as far as I know adjectives should be before the name but in this case the adjective "great" is after the name, is that grammatically correct?

[Anglika]

It is a very common form of descriptive indentifier, not simply an adjective, with or without an article - there are many historical figures who have this:

William the Conqueror
Harald Bluetooth
Olof the Brash
Ethelred the Unready
Edward the Confessor.
Eric the Child

[LwyrFirat]

Is it ok if we use for today's people, or is it special for historical figures, for ex is it ok to say "Anglika the Great"?

[Anglika]

You can, but it is rarely used seriously nowadays