God only knows I suppose.
In a narrow sense, those who have been baptized into Him, Father Son and Holy Spirit.
A broad sense (controversial) The Anonymous Christian
Anonymous Christianity means that a person lives in the grace of God and attains salvation outside of explicitly constituted Christianity — Let us say, a Buddhist monk — who, because he follows his conscience, attains salvation and lives in the grace of God; of him I must say that he is an anonymous Christian; if not, I would have to presuppose that there is a genuine path to salvation that really attains that goal, but that simply has nothing to do with Jesus Christ. But I cannot do that. And so, if I hold if everyone depends upon Jesus Christ for salvation, and if at the same time I hold that many live in the world who have not expressly recognized Jesus Christ, then there remains in my opinion nothing else but to take up this postulate of an anonymous Christianity
Lumen Gentium Those also can attain to everlasting salvation who through no fault of their own do not know the gospel of Christ or his Church, yet sincerely seek God and, moved by grace, strive by their deeds to do his will as it is known to them through the dictates of conscience." They went on to write, in Gaudium et Spes, "Since Christ died for all men, and since the ultimate vocation of man is in fact one, and divine, we ought to believe that the Holy Spirit in a manner known only to God offers to every man the possibility of being associated with this paschal mystery.
The Catechism of the Catholic Church teaches, “Those who through no fault of their own, do not know the Gospel of Christ or His Church, but who nevertheless seek God with a sincere heart, and, moved by grace, try in their actions to do his will as they know it through the dictates of their conscience—those too may achieve eternal salvation.”
Before becoming Pope Benedict XVI, Joseph Cardinal Ratzinger headed the Congregation for the Doctrine of the Faith. In this role, he issued, with the approval of Pope John Paul II, a document called Dominus Iesus. This document asserts the supremacy of the Catholic Church, while reiterating the Catholic Church’s acceptance of “anonymous Christianity.”
“Nevertheless, God, who desires to call all peoples to himself in Christ and to communicate to them the fullness of his revelation and love, “does not fail to make himself present in many ways, not only to individuals, but also to entire peoples through their spiritual riches, of which their religions are the main and essential expression even when they contain ‘gaps, insufficiencies and errors’”. Therefore, the sacred books of other religions, which in actual fact direct and nourish the existence of their followers, receive from the mystery of Christ the elements of goodness and grace which they contain.” (I, 8)
“Theology today, in its reflection on the existence of other religious experiences and on their meaning in God’s salvific plan, is invited to explore if and in what way the historical figures and positive elements of these religions may fall within the divine plan of salvation. In this undertaking, theological research has a vast field of work under the guidance of the Church’s Magisterium. The Second Vatican Council, in fact, has stated that: “the unique mediation of the Redeemer does not exclude, but rather gives rise to a manifold cooperation which is but a participation in this one source”.” (III, 14)
“With respect to the way in which the salvific grace of God — which is always given by means of Christ in the Spirit and has a mysterious relationship to the Church — comes to individual non-Christians, the Second Vatican Council limited itself to the statement that God bestows it “in ways known to himself”.” (VI, 21)