This is probably the German name ISE(N)GRIM. It is used as a poetic term for the fox and from the 18th cent. on also had the meaning "grumpy person". As a name it is usually explained as "iron helmet" (later influenced by "grim"), but it seems like it has not really been used as a given name in Germany.
This is taken from: Deutsches Wörterbuch von Wilhelm und Jacob Grimm Friedrich Kluge / Elmar Seebold, Etymologisches Wörterbuch der deutschen Sprache, Berlin 1995