Predestination and Reformed theology

If you think that believing in predestination is the definition of being "Reformed", then your version of Reformed theology could do without the Reformation, John Calvin, Guido de Bres, Ursinus, Olevianus, the Westminster Assembly, etc. You could be an Early or Medieval Christian instead, since predestination was alive (though frequently opposed) well-before the Reformation. Augustine of Hippo is one well-known proponent. A lesser-known advocate is Gottschalk of Orbais (mid-9th c.). Here is an excerpt from his Shorter Confession Concerning Double Predestination, slightly modified for readability from R. Scott Clark's translation (he also includes a short bio):

I believe and confess that God, omnipotently and unchangeably, has graciously foreknown and predestined holy angels and elect men to eternal life, and that He in like manner has, by his most just judgment, predestined [Satan], with all his apostate angels and also with reprobate men, who are his members, on account of their foreknown particular future evil deeds, to merited eternal death: this the Lord Himself affirms in His Gospel: "The prince of this world is already judged" (John 14:11).

It's better to recognize that predestination is a glorious component to "Reformed theology". It's far from being its defining doctrine, though.