John Bradford (1510–1555) was a prebendary of St. Paul's. He was an English Reformer and martyr best remembered for his utterance "There, but for the grace of God, goes John Bradford".
http://en.wikipedia.org/wiki/John_Bradford

The origin of the quote, “There but for the grace of God go I,” is attributed to John Bradford, but it is recorded a Bradford saying, “But for the grace of God there goes John Bradford.”

Bradford’s quote was prompted when he saw a group of criminals being led to their executions. Little did he know how true his quote, and the context in which he said it, was. John Bradford was an English preacher born in 1510 who at the age of 45 was executed by Queen Mary (of Bloody Mary fame) by burning at the stake. His crime was preaching the true Gospel of Jesus Christ and exposing England as a nation that had forsaken God. At that moment in his life, on July 15th 1555, the grace of God was sufficient for John Bradford as he gave up the ghost to enter an eternal paradise.
http://www.bibleornot.org/there-but-for-the-grace-of-god-go-i/