What is the role of “زَيْدٌ” in “جَاءَنِي زَيْدٌ وَهُوَ رَاكِبٌ”?

States of the Subject: Proper Names, Prior-Reference Article and Annexation

• Only expressing the riding state
• Naming the person who came
• Deleting the pronoun’s antecedent
• Turning the sentence into a question