  In the first part of this article, I briefly review early research activities
concerning strongly correlated electron systems, beginning with the discovery
of superconductivity and the first observation of a resistance minimum in
nominally pure Cu-metal, which was explained many years later by Kondo. I will
also address the antagonistic behavior of conventional (BCS) superconductivity
and magnetism. The main focus of this paper is on the discovery of non-BCS-type
superconductivity in the Kondo-lattice system CeCu$_2$Si$_2$, a prototypical
heavy-fermion metal. Here, the superconducting state is created by a periodic
lattice of 100% of magnetic Ce^3+ ions. Meanwhile, more than fifty lanthanide-,
actinide-, and transition-metal-based intermetallic compounds are known to
belong to the class of heavy-fermion superconductors. Finally, I will give my
personal view of the current knowledge of this kind of unconventional
superconductivity.
