Venerable (Blessed as of tomorrow) John Henry Newman is a hero of mine, perhaps, you might say, for obvious reasons. But in fact, he has had a special place in my life since I was a Lutheran seminarian, long before I followed his example and converted to Catholicism. So I am rather looking forward to tomorrow. The girls and I have already added JHN to our little bed-time litany of the saints, along with St Joseph and St Michael (my patrons), St Bernadette (their school patroness), and Blessed (soon Saint) Mary of the Cross.
But I was wondering this morning about "Convert Saints", by which I mean converts from other Christian traditions, saints who were baptised already before becoming Catholic. I know that there have been many from other religions, notably St Edith Stein and St Josephine Bakhita (I don't think St Paul or the other apostles count - they were not so much converted from Judaism - which was not a separate religion from Christianity at the time - as to a new sect within Judaism). St Augustine was a convert from Manicheanism, but that that wasn't really a form of Christianity.
A check on the internet gave me St. John Ogilvie (born into a Scottish Calvinist family in 1579), St Henry Morse (an English Protestant born in 1595) and St Elizabeth Ann Seton (born as an Episcopalian in 1774). Have there been any others than anyone knows about?