Respuesta :
It depends on how specific you want to be, but he was declared kaiser in 1871; more specifically, January 18th, 1871.
Wilhelm I was declared Kaiser of Germany in 1871.
Wilhelm I was the King of Prussia from 1861 until his death and also the first Emperor of the unified German Empire since 1871. Under his leadership as head of state, Prussia achieved the German Unification and consequently the establishment of the German Empire (modern Germany as we know it today, but with greater territory).