Diomedes is a very important member of the Achaian army who just can't seem to get any credit. Poor dude.
This is reflected not only in his peripheral status in scholarly treatments of the Iliad (with many even arguing that his night-raid with Odysseus wasn't part of the original text), but also from the fact that other Achaian warriors are constantly ragging on him and telling him he doesn't measure up to his father.
We at Shmoop think this is unfair. Not only is Diomedes the only Achaian who doesn't seem to care whether Achilleus is with them or not (obviously, there's a bit of ego involved here), but he's also the only character in the Iliad who deliberately takes on the gods in combat, once Athene removes the mist from his eyes. That's pretty hardcore.