Here is a great page if you want an intro. to the writing and thoughts of GK Chesterton. He was much more of an apologist for the Catholic Church specifically than CS Lewis was for any church but when Chesterton argues against anti-Christian schools of thought there is no better man to have on your side.
Every Christian would benefit from reading Everlasting Man and Orthodoxy
I think one thing that needs to be pointed out is that although Chesterton did write many works of Catholic Apologetics and social commentary, he also wrote terrific detective novels and short stories.
Chesterton is an "ecumenical figure" in the sense that his writing is not a Left Behind style of polemic. He is an example in many cases not of Christian literature, but rather good literature written by Christian.
I haven't read it yet, but his novel The Man Who Was Thursday is actually supposed to be considered to be serious literature in the academic sense.
I am actually going through his poetry right now for the sake of applying critical literary theories to them for class papers. He is pretty much ignored in academia so I am doing my part to give him a rebirth.