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