Setting history:

Instead of the Roman mystery cult of Mithraism being based on a flawed understanding of Zoroastrianism; a broadly equivalent cult (of Law) was established on the mostly modern (as of the third millenium) western interpretation and practice of the fealty to Marduk.

Clerics broadly preach the doctrine of the entire pantheon, but there are cults and orders within the Church that play favorites. Mithras / Marduk is additionally a popular patron of the lawfully aligned warriors in the West.

There aren’t any paladins in the Emain Ablach campaign yet, but if they do show up, they will be followers of Mithras.