Achaicus was a Corinthian Christian who according to the Bible, together with Fortunatus and Stephanas, carried a letter from the Corinthians to St. Paul, and from St. Paul to the Corinthians (1 Corinthians 16:17; cf. also 16:15).
By Eastern Orthodox Church tradition, Achaicus is also often numbered as one of the Seventy disciples, a group of early followers sent out by Jesus in Luke's gospel. The Biblical account does not mention the names of the seventy disciples, but various lists including Achaicus have been compiled since the 7th century, such as in the Orthodox Study Bible.
Achaicus is venerated as saint by Eastern Orthodox Church, Roman Catholic Church and other Christian Churches. In the Orthodox Church, he is commemorated with a feast day on June 15, with his companion Fortunatas. He is also remembered on the Synaxis of the Seventy Apostles on January 4.