Paul was at different times in differing roles, sometimes simultaneously: cross-cultural missionary traveling from region to region, evangelist in a city, pastor of a local congregation, counselor, coordinator of the affairs of churches in an interregional framework (the bishop or superintendent of today), leader of a missionary team, teacher of co-workers, teacher of new converts, theologian, author of theological writings, author of hymns (perhaps), and leather worker who needed to earn money. A missionary who explores new territory without any existing models, who is ready to value co-workers more than self, who is prepared to carry the cross daily not the “head of department” or an “office boss.”
A missionary tackles the task at hand, using every opportunity for preaching the good news of Jesus Christ, and striving to nurture new believers in any way necessary.
OK, none of us come close. Let's make the list simpler and realistic. What does an apostle do?
An apostle takes the gospel to people who haven't heard it. An apostle forms new communities of disciples. An apostle keeps returning until those communities are viable. An apostle moves on to new unreached fields, multiplying disciples and churches.
If you do that, you're an apostle (the missionary/missional kind not the writing scripture kind). But don't put it on your business card. Let the fruit of your ministry speak.