Paulus. It's a second-declension masculine noun, so the forms are:
- nominative: Paulus (sentence subject)
- vocative: Paule ("O Paul!")
- genitive: Pauli ("of Paul")
- dative: Paulo ("to/for Paul")
- accusative: Paulum (object of verb or of some prepositions)
- ablative: Paulo ("by, with, from Paul")
