Thersites

Shakespeare has lots of characters who comment on the actions of others (and sometimes on their own).   He has impertinent upstarts--women, jesters and suchlike--who choose not to know their place.  But I think Thersites in Troilus and Cressida is the only upstart commentator who virtually dominates his show.  

Thersites is a fully-developed character in Homer's Iliad (in book II);  more fully than I remembered:

[211] Now the others sate them down and were stayed in their places, only there still kept chattering on Thersites of measureless speech, whose mind was full of great store of disorderly words, wherewith to utter revilings against the kings, idly, and in no orderly wise, but whatsoever he deemed would raise a laugh among the Argives. Evil-favoured was he beyond all men that came to Ilios: he was bandy-legged and lame in the one foot, and his two shoulders were rounded, stooping together over his chest, and above them his head was warped, and a scant stubble grew thereon. Hateful was he to Achilles above all, and to Odysseus, for it was they twain that he was wont to revile; but now again with shrill cries he uttered abuse against goodly Agamemnon. With him were the Achaeans exceeding wroth, and had indignation in their hearts. 

[224] Howbeit with loud shoutings he spake and chide Agamemnon: "Son of Atreus, with what art thou now again discontent, or what lack is thine? Filled are thy huts with bronze, and women full many are in thy huts, chosen spoils that we Achaeans give thee first of all, whensoe'er we take a citadel. Or dost thou still want gold also, which some man of the horse-taming Trojans shall bring thee out of Ilios as a ransom for his son, whom I haply have bound and led away or some other of the Achaeans? Or is it some young girl for thee to know in love, whom thou wilt keep apart for thyself? Nay, it beseemeth not one that is their captain to bring to ill the sons of the Achaeans. Soft fools! base things of shame, ye women of Achaea, men no more, homeward let us go with our ships, and leave this fellow here in the land of Troy to digest his prizes, that so he may learn whether in us too there is aught of aid for him or no—for him that hath now done dishonour to Achilles, a man better far than he;  for he hath taken away, and keepeth his prize by his own arrogant act. Of a surety there is naught of wrath in the heart of Achilles; nay, he heedeth not at all; else, son of Atreus, wouldest thou now work insolence for the last time." 

[243] So spake Thersites, railing at Agamemnon, shepherd of the host. But quickly to his side came goodly Odysseus, and with an angry glance from beneath his brows, chid him with harsh words, saying: "Thersites of reckless speech, clear-voiced talker though thou art, refrain thee, and be not minded to strive singly against kings. For I deem that there is no viler mortal than thou amongst all those that with the sons of Atreus came beneath Ilios. Wherefore 'twere well thou shouldst not take the name of kings in thy mouth as thou protest, to cast reproaches upon them, and to watch for home-going. In no wise do we know clearly as yet how these things are to be, whether it be for good or ill that we sons of the Achaeans shall return. Therefore dost thou now continually utter revilings against Atreus' son, Agamemnon, shepherd of the host, for that the Danaan warriors give him gifts full many; whereas thou pratest on with railings. But I will speak out to thee, and this word shall verily be brought to pass: if I find thee again playing the fool, even as now thou dost, then may the head of Odysseus abide no more upon his shoulders, nor may I any more be called the father of Telemachus, if I take thee not, and strip off thy raiment, thy cloak, and thy tunic that cover thy nakedness, and for thyself send thee wailing to the swift ships, beaten forth from the place of gathering with shameful blows." 

[265] So spake Odysseus, and with his staff smote his back and shoulders; and Thersites cowered down, and a big tear fell from him, and a bloody weal rose up on his back beneath the staff of gold. Then he sate him down, and fear came upon him, and stung by pain with helpless looks he wiped away the tear. But the Achaeans, sore vexed at heart though they were, broke into a merry laugh at him, and thus would one speak with a glance at his neighbour: "Out upon it! verily hath Odysseus ere now wrought good deeds without number as leader in good counsel and setting battle in army, but now is this deed far the best that he hath wrought among the Argives, seeing he hath made this scurrilous babbler to cease from his prating. Never again, I ween, will his proud spirit henceforth set him on to rail at kings with words of reviling."

 That's the A.T. Murray translation, happily public-domained here.  It's hard to imagine what Murray thought he was achieving with this constrained archaism, but for this particular passage I'd say it works pretty well--there's an odd fairy-tale quality to the episode, perhaps more suited to the Odyssey than the work in which it is found.

Homer never actually specifies that Thersites is a (mere) commoner, but it is said that he is the only figure in the Epic without a patronymic--so, a man of no breeding (Ashland put in him the garb of an enlisted man, set off against all the officers).  Michael Gilleland picks up a provocative bit of theological context:

Those closest to the gods in Homer are not the poor and the meek, but the strong and the powerful; the godless one, i.e. the one who is shunned by the gods, upon whom they do not bestow any gifts, is Thersites.

So Bruno Snell, The Discovery of the Mind, chapter 2 (The Olympian Gods).

  For the tradition of Thersites through the ages, you can begin with an admirable Wiki here.