The occasion of Martin Luther King Jr.'s birthday leads me to this short piece of advice to Christians: be careful not to try and claim historical figures as "one of us", if there's evidence they were not.
I feel we evangelicals have a bad habit of trying to claim various historical figures for ourselves. In the 1980s, there was a book titled The Light and the Glory, which as much as said that the U.S. was a new promised land. It painted Christopher Columbus as an anointed servant of Christ. But history tells us that Columbus was either, a nominal Roman Catholic (as nearly all western Europeans were), or a sincerely ardent one. The people he cruelly killed and enslaved probably didn't see him as a servant of God.
Dietrich Bonhoeffer was not an evangelical Christian, either; when you read his training and personal beliefs, he was a rigorously moral but mostly-liberal Lutheran of his day. Martin Luther King wasn't an evangelical, and (based on his own written beliefs from his seminary papers) was not a Christian during his years at Crozer Theological Seminary. He was very liberal, theologically, though it's possible he genuinely trusted in Christ later in his adult life, and friends have told me that was the case. I hope that's true.
C.S. Lewis' beliefs were a mixture of the gospel, plus some Anglican Catholicism, plus some Plato thrown in for good measure. In Lewis' case, I expect to see him with the Lord, but I have to weed out certain ideas in his writings. He was no British Puritan. In the same sense I also expect to see George Washington with the Lord, based on his confessions of faith, but Washington, like Lewis, wasn't doctrinally speaking a Puritan either (unlike another founding father, John Witherspoon).
The fact that various religious or religiously-inclined people from history were not evangelicals doesn't mean they were all bad. Many of them were devout, like Cornelius the centurion was devout (Acts 10). I think we should be conservative in the way we think about American historical figures, and not claim more for them than the evidence supports.