Who is a Christian missionary?
Lumen Gentium, the Dogmatic Constitution of the Church promulgated by the Second Vatican Council, states clearly the mission of the Church, "When Jesus, who had suffered the death of the cross for mankind, had risen, He appeared as the one constituted as Lord, Christ and eternal Priest, and He poured out on His disciples the Spirit promised by the Father. From this source the Church, equipped with the gifts of its Founder and faithfully guarding His precepts of charity, humility and self-sacrifice, receives the mission to proclaim and to spread among all peoples the Kingdom of Christ and of God and to be, on earth, the initial budding forth of that kingdom. While it slowly grows, the Church strains toward the completed Kingdom and, with all its strength, hopes and desires to be united in glory with its King." (cf. paragraph 5)
Gaudium et Spes, the Pastoral Constitution of the Church, continues this line of thinking, "The Church, sent to all peoples of every time and place, is not bound exclusively and indissolubly to any race or nation, any particular way of life or any customary way of life recent or ancient. Faithful to her own tradition and at the same time conscious of her universal mission, she can enter into communion with the various civilizations, to their enrichment and the enrichment of the Church herself." (cf. paragraph 58)
Thus, the Church, in her very nature is a missionary community. Furthermore, since the Church is the entirety of the people of God, as these documents from Vatican II clearly illustrate, each and every person who is in communion with the Church has as his or her vocation to be a missionary, to proclaim the Good News of Jesus Christ in his or her life to the best of their abilities.
Other Protestant churches designate certain members of their community to go out to do missionary work in their local community or in exotic locales. Oftentimes, Catholics tend to pigeonhole missionaries those men and women doing similar work on behalf of our Church, but we, as Catholics, died with Christ in the waters of Baptism and, therefore, should lead a Christ-like life of bringing others to an experience and understanding of God's limitless love and mercy through our virtue, our example, and our transparency.