This is a naive question but if you've got a funded startup, you're not the owner are you?
Maybe pedantic, but here goes: If you have given away so much as a single share, the usual phraseology is that you are "part-owner", because you own only a part. Saying "The owner" implies there is only one, which is false.
If you declare to the other shareholder that you are the owner, you might find an interesting reaction.
Good luck.