And the original settlers board game - Catan - is of course also German.

The board game came out after the first computer game. The two are not related.

Oh.. i didn't know! Maybe the relation is still there, inverted?

According to Wikipedia, Klaus Teuber started designing the board game years before the computer game was released, so it's probably not a major source of inspiration. He did change the name (adding "of Catan") so people wouldn't mistake one for the other.

Die Siedler (the plural is the same as the singular), but yeah.