Vytautas of Lithuania (late fourteenth - early fifteenth century) was baptized three times, if I remember correctly.
Apparently Vytautas was baptized three times: first Orthodox, then twice as a Catholic.
His cousin, Jagiello, whom he spent a couple of decades feuding with after J. probably bumped off his father Kestutis, was baptized Orthodox and then baptized Catholic many years later.
Ah, how I miss my days as a Church historian looking up all of this stuff!