I think you mean Vega, not M. Bison. Fixing the tags.

It's Vega for the Japanese version, but in the US version it's M. Bison... It's kinda weird...

Other difference: (US/Japanese)
Boxer: Balrog/M. Bison
Masked Weird: Vega/Balrog
Shadaloo Boss: M. Bison/Vega

The reason for the Balrog/Vega/M. Bison change is this:
Balrog (Here) is Mike Bison in Japan. Who was a ultra famous black boxer in America in the early 90s? Hmmm...He had his own version of Punch Out on the NES...Ah, Mike Tyson!
Do you want Tyson to sue/beat/bite the fuck out of you? No! So, they changed three names around to where it fit somewhat.
History my younger brethren, History!

I hope this is her second alternate costume in Super SFIV.

I seem to recall that it led to them being referred to as 'Boxer' 'Tyrant' and 'Claw' in international Street Fighter communities to avoid confusion.

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egnirys69 said:
Haven't heard Tyrant yet ... always hear Dictator instead.

Whoops, that's correct. I misremembered.