Joseph Stalin trained to be a priest for five years.

At age 14, Stalin was sent by his mother to Tiflis Theological Seminary in what is now Tbilisi, Georgia. Young Joseph had earned a scholarship there and intended on eventually becoming a priest in the Georgian Orthodox Church. This didn't quite work out, as Stalin got caught up in a secret socialist society called Messameh Dassy. After five years of sneaking out to attend revolutionary meetings, the seminary finally kicked him out. It is not known how much of an effect these years had on his later career, but it can't be denied that these years had a great influence on Stalin's political future.
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Learn more about Joseph Stalin in this biography on PBS.