A proper name is definite, but the hearer may know more than one person with that name. A description can distinguish the intended individual.
زَيْدٌ التَّاجِرُ عِنْدَنَا
Zayd the merchant is with us.
If several men named Zayd are familiar, «التاجر» resolves which one is meant. The proper name was already definite; the epithet is not making an indefinite noun definite. Rather, it removes ambiguity within a definite reference.
Opening interactive controls...
Description and Emphasis of the Subject: Rhetorical Purposes and Fine Distinctions
A proper name is definite, but the hearer may know more than one person with that name. A description can distinguish the intended individual.
زَيْدٌ التَّاجِرُ عِنْدَنَا
Zayd the merchant is with us.
If several men named Zayd are familiar, «التاجر» resolves which one is meant. The proper name was already definite; the epithet is not making an indefinite noun definite. Rather, it removes ambiguity within a definite reference.