Stein um Stein Lyrics

Lyric discussion by atchi 

Cover art for Stein um Stein lyrics by Rammstein

I absolutely agree with the comments about the protagonist wanting to keep a lover all to himself. If you have a look at Klavier as well, there's a definite jealousy theme coming through - he wants to keep the girl all to himself, even if that means effectively building a jail for her.

Define "protagonist".