Theodore Stratelates
The patron saint of Venice before the relics of Mark were (according to tradition) brought to the city in 828 was Theodore and the Doge's original chapel was dedicated to that saint, though, after the translation of the relics, it was superseded as his chapel by the church of St Mark. This may be either Theodore of Amasea or Theodore Stratelates, but the Venetians do not seem to have distinguished between them.