"A forty year journey"

More than one hundred years ago, Albert Einstein published his Theory of General Relativity(GR). One year later, Karl Schwarzschild solved the GR equations for a non-rotating, sphericalmass distribution; if this mass is sufciently compact, even light cannot escape from withinthe so called event horizon, and there is a mass singularity at the center. The theoreticalconcept of a `black hole' was born, and was rened in the next decades by work of Penrose,Wheeler, Kerr, Hawking and many others. First indirect evidence for the existence of suchblack holes in our Universe came from observations of compact X-ray binaries and distantluminous quasars. I will discuss the forty year journey, which my colleagues and I have beenundertaking to study the mass distribution in the Center of our Milky Way from ever moreprecise, long term studies of the motions of gas and stars as test particles of the space time.These studies show the existence of a four million solar mass object, which must be a singlemassive black hole, beyond any reasonable doubt.