What is Othello's religion? Has he converted to Christianity? What was he before?

And then for her
To win the Moor, were't to renounce his baptism,
All seals and symbols of redeemed sin...
(2.3.342-44)

There's Iago, in Act 2, Scene 3, telling us that Othello has indeed been baptised. And yet, as a Moor, it seems highly unlikely that Othello could have been born a Christian, as Moors were Muslim and circumcised. Othello has been converted to Christianity, as his own words seem to suggest a little later in the play:

"For Christian shame put by this
barbarous brawl!"

"Are we turned Turks?"

So the logical conclusion to draw seems to be that Othello was a Muslim and is now converted to Christianity.

Critic Ian Doescher, however, seems to have a different view:

...[it] depends on when the play is set.  Muslims had control in Sicily in the middle 1400s, and therefore if the play is set before that time we may be prone to believe that Othello is a Muslim.  It is likely, though, the play is meant to be set after Muslim control in Sicily.  One reason is that Shakespeare's source for the play is an Italian play called "Heccatommithi," published in 1565, well after the Muslim control.

Also, considering that Othello is fighting the Turkish fleet, it seems more likely that he is Christian, as he is fighting for the Christian cause against the Muslims.  Finally, if the play is indeed set after the 1400s, it is unlikely that a Muslim would be allowed a position of nobility in a Christian society, especially one that had recently rid themselves of Muslim control.

Othello is still, then, most probably a Christian. And, as David Basch has written, Othello's name even seems to confirm that he is indeed a Christian - it may even be a name he assumed at baptism:

Here again, Othello's name would confirm this since, as Florence Amit has noted, the name means in Hebrew "his sign of God," a "sign" which scripture identifies circumcision (a sign in the flesh). This name link to circumcision is clearly pertinent since Othello's circumcision plays a central part in the words Othello uses in his final speech before thrusting his sword into himself, "I took the circumcised dog and smote him THUS."