It is arguable that Plato is the most influential of philosophers on Christianity, and especially Christian theology. There are two caveats to bear in mind, however.
Plato’s influence was almost always indirect, having been mediated by neo-Platonism, to which we will come when we have studied Aristotle.
Plato was adapted and subdued as much as he was accepted and used. The Jewish tradition had many ideas of its own, some of which overcame Plato’s in the development of Christian thought, some of which were overcome, and some of which combined in fascinating ways with Plato’s.
With these qualifications in mind, here are some of the areas of influence.
The Apologists: Christian Doctrine as Purified, Definitive Greek Philosophy
God as Immutable: Forsaking Hebrew Ideas
The (Eventual) Triumph of Dualism: Nature vs. Spirit, Body vs. Mind
Creation: Forms are the Creative Thoughts of God; Prepares way for Ex Nihilo; Inspires Neo-Platonic Hierarchy of Being
Incarnation: Jesus Christ as Perfect Instantiation of The Logos
Society: The Great Accidental Social Experiment Based on the Republic
Mysticism: The Beatific Vision (of the Forms)