It's like this:
King Koopa in Japan
Bowser in US.
In US, he's also called King Bowser and King of the Koopas. Therefore,
Full title: King Bowser Koopa.
They simply call him by his last name, just like they call Peach only by her first name:
Peach in Jap.
Princess Toadstool in US, but also Princess Peach.
Solution? Princess Peach Toadstool.
Eh, that was completely unnessesary to go thru all that explaining, wasn't it? Oh well...
The 1964th person