Philip II is best know to history for being the father of Alexander the Great. However, Philip was a great conqueror in his own right, laying the basis for Alexander's greater conquests.
Before Philip, Macedonia was divided and weak. But Philip transformed it. Philip used superior military tactics, notably the effective use of cavalry and more lightly armored hoplites with long spears instead of swords, to defeat Greece in 338 BCE. He was acknowledged as hegemon of all Greece except for Sparta.
Philip was assassinated in 336 BCE and was therefore unable to pursue his dream of conquering Persia. That fell to his son.
Thus, Philip is important both as the father of Alexander and as the king who made Macedonia strong.