When I first began learning German, I was told this: There are only four irregular verbs in the German language. This statement is accurate only dependant on one's point of view. Some will say that there are many more, whereas I would say there are, in fact, none. If I were to relent, and say there was a single irregular verb in the entire language, this would be it:
sein to be
ich bin I am
du bist you are (thou art)
er ist he is
sie ist she is
es ist it is
wer ist who is
man ist one is
wir sind we are
ihr seid you are (ye are)
sie sind they are
Sie sind you are (stranger or strangers)