Mark Twain, portrait from the early-1850s. Quintessential American author. Wildly humorous, brilliantly observant, clever and socially aware. Ahead of his time. If you've never read any Twain, start with Huck Finn.
C S Lewis was\is primarily for me a theologian and Christian apologist. He was also a novelist - "The Chronicles of Narnia" "The Space Trilogy" "The Lion, the Witch and the Wardrobe" and his Christian writings "Mere Christianity" "The Problem of Pain" "God in the Dock" "The Screwtape Letters". Arguably the most influential Christian writer in my life. I've both learned so much, and have taught from his books.
Nelson Mandela (affectionately known as Madiba) served as President of South Africa from 1994 to 1999, the first ever to be elected in a fully representative democratic election. He's also known for his relaxed and colourful T-shirts (which we love!)