Who introduced primogeniture into East Frisia?

Johan I of East Frisia (1506–1572) was a member of the house of Cirksena and a non-reigning Count of East Frisia and later imperial governor of Limburg. His father, Edzard the Great, had introduced primogeniture in the county of East Frisia, so that his older brother Enno II of East Frisia inherited the county alone and he had to hold back. Despite his ambitions, he always acknowledged his brother's rights and did not dispute the inheritance.

Edzard the Great