The first convert of Paul is not specified in the Bible. The first mentioned is Sergius Paulus.

I think, his name was Lucius? (premomen, dubious) Sergius (nomen) Saulus (cognomen): the most important is SERGIUS; Saulus (Saul) was also his personal Jewish name (cf. Flavius Iosephus, Cassius Dio, etc.) -- all very typical for the new (provincial) citizens. When Saul met his Roman relative, proconsul Lucius Sergius Paulus (the elder member of Tribus Sergia), and became his friend, he took his cognomen and became Paulus -- in Rome it was not unusual, and it strengthened St.Paul's Roman citizenship.

Prof. Elena G. Rabinovitch, St.Petersburg

Several surnames are to found in the New Testament, such as Pontius Pilate. The fifth book, Acts of the Apostles, names Porcius Festus, Simeon Niger, Judas and James Barsabbas, Claudius Lysias, and Sergius Paulus.

Sergius Kagen died in 1964.

Sergius Kagen was born in 1909.