Flavius and Murellus are two snooty conspirators against Caesar. In the opening scene, they catch a bunch of commoners celebrating Caesar's victorious return to Rome and try to give them a spanking for not being hard at work. Check out what Flavius says (and pay attention, because these are the very first lines spoken in the play):
Hence! home, you idle creatures get you home:
Is this a holiday? what! know you not,
Being mechanical, you ought not walk
Upon a labouring day without the sign
Of your profession? Speak, what trade art thou? (1.1.1)
Obviously Flavius is miffed that Caesar is such a rock star among the plebeians. It also seems pretty clear that he doesn't have any respect for the common folk in Rome, which draws our attention to the fact that, even though Rome may be a Republic, guys like Flavius and Murellus don't necessarily think all Romans are created equal. This raises an important question in the play: Who should get to decide the rules of government? Later, when we learn that Flavius and Murellus have been "put to silence" (1.2.14) for defacing pictures of Caesar, we wonder whether Caesar might really be the tyrant the conspirators say he is.