What we have learned from SN 1987A about supernova explosions

SN 1987A celebrated its 20 year anniversary on February 23. In this talk I will review the immense importance of SN 1987A for the understanding of the collapse of massive stars in general. In particular, the mechanism behind the collapse and explosion of the core will be summarized, including recent new developments of this longstanding problem. The nucleosynthesis and the connection to other classes of supernovae and gamma-ray bursts will be discussed. Finally, I will also discuss the exciting ongoing collision between the ejecta and the circumstellar ring of SN 1987A which provides us with a unique laboratory for both shock physics and the acceleration of high energy particles.