Henri Poincaré (1854-1912) was one of the most prolific scientific authors of all times. Born and educated in Nancy he showed already very young a wide interest in literature, natural phenomena, geometry, politics and many other topics. When he was around twenty years old, he made a definite choice for mathematics, physics and astronomy. He pursued his education in Paris at the Ecole Polytechnique and the Ecole des Mines. For a brief period he was a mining engineer, but switched to a mathematics lecturing position in Caen (Normandy) and shortly afterwards to Paris where he taught mathematics, celestial mechanics and mathematical physics. Already famous among scientists, he became well-known to the general public by his books of philosophical essays published by Flammarion.
It is remarkable that Poincaré started whole new fields: dynamical systems (with strong interaction between geometry and analysis), automorphic functions, topology; he was a founder of Special Relativity, together with Lorentz and Einstein. After surveying his achievements, we will discuss part of his work, in particular the Price Essay for King Oscar II which stands at the beginning of chaos theory and in general his contributions to dynamical systems theory.