Plain form of でしょう, so used within a sentence, or at the end of the sentence if the speaker is talking in plain form.
An auxiliary indicating the speaker's conjecture which is not based on any particular information or evidence.
This is really two different usages stuck in one entry ...
I'm confused, do you have to add か or not?
か end of the sentence is sometimes add to express suspition or question. If there is どこ、何、どう etc in the sentence, you can omit か as you can still know that is a question. But like #4779, if you omit か, it is not so clear if you have doubt or you affirmed.
だろう is the plain form of でしょう so while it may be used in many yakuza movies, it's just that the characters are speaking in plain form. If they were to say でしょう when speaking amongst each other (people at the same level), it would sound too polite for the character, and therefore strange.
How did #484 got in there?
Would I be correct in assuming that rough guys use this when they don't really have to, to sound tough? I notice yakuza and the like use it a lot.
Clay, you are not correct.
In the first example it's used as a way to agree with some flattery (possibly without seeming too boastful).