In his historic address to Congress yesterday Pope Francis mentioned two American Catholics who it's fair to say aren't household words – Thomas Merton and Dorothy Day. So who was Thomas Merton and why did the Pope think he was important enough to mention?

Thomas Merton (1915-1968) was an American Catholic poet and social activist. A Trappist monk, he wrote more than 70 books including the bestselling spiritual autobiography The Seven Storey Mountain (1948).

Merton's spirituality was intensely mystical, drawing not just on Christian traditions but on Eastern religions as well, though he was an orthodox Christian.

His mother died when he was six years old and he grew up with his father in the US, France and England.

Before attending university at Cambridge he went on a tour of Europe, including Rome, where his attraction to Catholicism first began to grow. He was received into the Church in 1938 and was received into the Cistercian Order as a novice at the Abbey of Gethsemani in Kentucky in 1942.

He taught and wrote widely, preaching peace, racial tolerance, and social equality. He was sympathetic to the new reform movements in Latin America associated with Liberation Theology, writing to one theologian: "The world is full of great criminals with enormous power, and they are in a death struggle with each other. It is a huge gang battle, using well-meaning lawyers and policemen and clergymen as their front, controlling papers, means of communication, and enrolling everybody in their armies."

However, it is for his deep insight into the human nature and the ways of God that he will be remembered.

In his address to Congress Pope Francis said: "Merton was above all a man of prayer, a thinker who challenged the certitudes of his time and opened new horizons for souls and for the Church. He was also a man of dialogue, a promoter of peace between peoples and religions."

Merton died tragically early, electrocuted in Bangkok by an electric fan as he stepped out of a bath. Here are ten of his finest quotes:

1. The beginning of love is the will to let those we love be perfectly themselves, the resolution not to twist them to fit our own image.

2. Our job is to love others without stopping to inquire whether or not they are worthy. That is not our business and, in fact, it is nobody's business. What we are asked to do is to love, and this love itself will render both ourselves and our neighbours worthy.

3. Do not depend on the hope of results. You may have to face the fact that your work will be apparently worthless and even achieve no result at all, if not perhaps results opposite to what you expect. As you get used to this idea, you start more and more to concentrate not on the results, but on the value, the rightness, the truth of the work itself.

4. Instead of hating the people you think are war-makers, hate the appetites and disorder in your own soul, which are the causes of war. If you love peace, then hate injustice, hate tyranny, hate greed - but hate these things in yourself, not in another.

5. A man knows when he has found his vocation when he stops thinking about how to live and begins to live.

6. Life is this simple: we are living in a world that is absolutely transparent and the divine is shining through it all the time. This is not just a nice story or a fable, it is true.

7. Reason is in fact the path to faith, and faith takes over when reason can say no more.

8. Souls are like athletes, that need opponents worthy of them, if they are to be tried and extended and pushed to the full use of their powers, and rewarded according to their capacity.

9. The greatest need of our time is to clean out the enormous mass of mental and emotional rubbish that clutters our minds.

10. Many poets are not poets for the same reason that many religious men are not saints: they never succeed in being themselves. They never get around to being the particular poet or the particular monk they are intended to be by God. They never become the man or the artist who is called for by all the circumstances of their individual lives. They waste their years in vain efforts to be some other poet, some other saint...They wear out their minds and bodies in a hopeless endeavor to have somebody else's experiences or write somebody else's poems.

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