I know this will never happen for all sorts of reasons, but let's have a bit of fun here and just imagine, what if; Master Chief was in Brawl!! 

Why would Nintendo agree?  Master Chief vs Mario (vs Sonic) would get mainstream press coverage money couldn't buy.  MC alone would also likely add 1 million+ sales in NA.   

Why would Microsoft? Street credit in Japan!  Halo in Brawl could boost Halo 3 (and 360) sales and recognition in Japan, and to a lesser degree Europe.  It'd only boost Brawls sales in NA.

 If this did happen, what effect would it have?  To sales? Hype? Sony?

And guys (and girls) this is just for fun, so don't take it too seriously.

Mario > MC

If (and this is a *huge* if) Halo DS was announced between now and February I wouldn't be surprised in any way at all to see Master Chief in Brawl. I have my reasons for considering this which I can explain at a later date, but for now, I think it's still possibility.

If he were in it though, sales for the game would go up by a minimum of 2 million.

If he were in it, I would only beat on him for the first week. I would tear him a new hole with every other character. Even Kirby.

Wow serious I thought Soriku made this 'IF' thread;

OT: I don't think he will be there, if he would be in it I will do the same like Homelesscarl.

Man then all of the other charcters would get their asses handed to them constantly. Ya can't beat the cheif.

Actually it would be pretty cool to see a samus chief fight.

But the chief uses guns and they are a big no no in Smash.

SSBB: Start another fight. I think it would be cool, I love plasma granades and I will kick his ass so many times with Samus that he will not appear again in a SSB game. Add 2 million to the SSBB total sales. His final smash will be something like Flood invation!

I present to you:

rocket launcher

Land mine


neck snap


gun


and considering that Samus, Link, Fox, and Pit will all be mainly ranged characters or have a good amount of ranged attacks I don't see a problem with another ranged character (especially one with sticky grenades).

-edit-
Though I do have a hard time imagining what his final smash would be.  It wouldn't be a flood invasion (since he doesn't really control them) and fox already has a tank so no Scorpion.  I guess he could call in support from a Warthog or more than likely a Pelican.  Actually, what could be cool is if the Arbiter came out of cloaking and helped him.

^^ Sticky grenades! Awesome.... oh wait... they're already in brawl. Strange...

Big guns!.

This is the bigger one(scary I know)