1) This is an abbreviation of the name in Dutch. As far as I can see, it happens in 2 steps: Cornelius -> Krelis -> Kees 2) "Dutch names can be very difficult to figure out. There are two kinds of Dutch diminuitives: the sh ortened Dutch name and the endearing Dutch name. The shortened name was used by the Dutch for both males and females. The endearing diminuitive was used exclusively for female names. This diminuitive form attached to female names as an expression of endearment was formed by adding the suffix -je or -tje. As well, -je, -tje, -ie and -ke are also additions to a child's name." "Following is a list of some Eng lish names with their Dutch equivalents, including both shortened and diminuitive Dutch forms when known. !" "English Names: Cornelis | Cornelius Dutch Equivalent Names: Cornelis Shortened Dutch Names: Krelis | Nelis | Kees | Cees | Cor" Source and further information: http://www.olivetreegenealogy.com/nn/names.shtml 3) "In the course of the Middle Ages names derived from Saints are getting more common than their Germanic counterparts. From the 12th century onwards it became a custom that the child received a Christian name, even though some Christian names like "Gertrude" and "Hubertus" were in fact of Germanic origin. The direct influence of the church on the transition from Germanic to Christian names must not be overestimated. Before the council of Trent (1545–1563), the Roman Catholic church did not have any regulation of the practice of naming children. There are thought to have been a number of reasons the Christian names gained the upper hand, such as the crusades, the larger ecclesiastical influence and the appearance of mendicant orders (such as the Franciscans and Dominicans) and most importantly, the veneration of saints and the appearance of patron saints. But apart from the religious influence it is believed that fashion was the main reason to give one's child a Christian name. With the emergence of flourishing cities all over the Low Countries, the citizens, especially the wealthy ones, were what we would call trend-setters in contemporary times. In these times some "typically" Dutch names like "Kees" (Cornelis), "Jan" (Johannes) and "Piet" (Petrus) emerge." Source and further information: http://en.wikipedia.org/wiki/Dutch_name