He is Half Jewish (Father) and was born in Muiderberg, a village about 15 kilometers east of Amsterdam. His father sold herring in the local market and as time went on he would sell trinkets by his sons games. In addition he would dress as Santa Clause before Christmas to make extra money. During the war his father would hide himself as a none Jew, but he still has many stories of almost being caught by the Natzi's. After Sjaak's mother died, his father got remarried to a women 30 years younger than him. Sjaak and his half Brother stop communicating after the passing of their father.
Nicknamed Mr. Ajax, he played for Ajax Amsterdam a total of almost 600 matches, a record for the club.