Stephanas was the first person Paul evangelized in Achaia and led to believe in Jesus. He was Paul's co-worker in the Corinthian church.
1 Cor 16:15Now I urge you, brothers and sisters—you know that the household of Stephanas were the first converts in Achaia, and they have devoted themselves to the service of the saints—1 Cor 16:16to submit to such as these, and to every co-worker and laborer.1 Cor 16:17I rejoice at the coming of Stephanas and Fortunatus and Achaicus, because they have made up for your absence;
He was also the only person Paul personally baptized.
1 Cor 1:16(I did baptize also the household of Stephanas; beyond that, I do not know whether I baptized anyone else.)