From the beginnings of human society eggs have played a role in both pagan as well as Christian rituals.
The egg was a fertility symbol. In Christianity the egg is a symbol of the Resurrection. The first painted eggs have been dated to the 13th Century. In fact, all of the traditions we have today about Easter eggs can be traced back to a purely practical use rather than to a ritual meaning. In previous centuries people also refrained from eating eggs during the 40 days of Lent. Since the hens continued to lay eggs during this period, stocks of eggs built up which were painted during the Easter holidays.
(Source: Markus Nowaks, Katholische Sonntags Zeitung [Catholic Sunday Newspaper], 22/03/2008)
The origins of Nestler Easter eggs go back to the year 1894.