Rome Latinised the Greek Kallimachus to be Callimachus and through the passage of time, it has entered the english vocab starting with the letter 'C'. This web site uses the orginal gramma.
He might be one of the most important forgotton identities in the ancient Greek world. His postion as polemarch of Athens during the Battle of Marathon, made him ultimately supreme commander of the Athenian forces. His role as polemarch for today's reader should be seen along the lines of 'elected king', it might be hard for us today to image a king being elected, but Athens was a fully fledged democracy all positions were voted by all the elegible male citizens of Athens. So for Kallimachus to be elected polemarch he would have to have completed some monumental task for the male citizens of Athens to overlook their petty squables between tribes to pick him, and indeed we find one written on the 'Monument to Kallimachus' where he is announced victor at the Panathenaic Games. Therefore, we can assume he is the best athelete Athens has, no better man in Athens to lead the hoplite army into battle.
Artwork: An artist's impression of the killing of Kallimachus at the burning of the ships, at the Battle of Marathon.
Nothing is known of his earlier life and what little we know of him comes mostly from Herodotus' book The Histories.
Even though there would have been much arguing, voting and negotiating in Athens during the initial Persian invasion, the final military say was Kallimachus'. As polemarch that was his duty, governed by law. During the envoy to Sparta, the decision to march out to meet the Persians at Marathon, the route taken to meet them, the 10 days lying in wait to strike at the Persians while at the sacred olive grove of Athena, the battle formation and the final rush into battle.
Miltiades gets alot of the credit for the Athenians actions at Marathon, and no dobut he had alot of say in what was going on at the time, but he was only one of ten generals, all equal in the army, but all were answerable to the Polemarch.
Herodotus recorded the speech Miltiades gave to Kallimachus to convince him to vote for war against the Persians.
" With thee it rests, Kallimachus, either to bring Athens to slavery, or, by securing her freedom, to leave behind thee to all future generations a memory beyond even Harmodius and Aristogeiton. For never since the time that the Athenians became a people were they in so great a danger as now. If they bow their necks beneath the yoke of the Medes, the woes which they will have to suffer when given into the power of Hippias are already determined on; if, on the other hand, they fight and overcome, Athens may rise to be the very first city in Greece. How it comes to pass that these things are likely to happen, and how the determining of them in some sort rests with thee, I will now proceed to make clear. We generals are ten in number, and our votes are divided; half of us wish to engage, half to avoid a combat. Now, if we do not fight, I look to see a great disturbance at Athens which will shake men's resolutions, and then I fear they will submit themselves; but if few fight the battle before any unsoundness show itself among our citizens, let the gods but give us fair play, and we are well able to overcome the enemy. On thee therefore we depend in this matter, which lies wholly in thine own power. Thou hast only to add thy vote to my side and thy country will be free, and not free only, but the first state in Greece. Or, if thou preferest to give they vote to them who would decline the combat, then the reverse will follow .� 
Kallimachus ageed with Miltiades for war.
During the battle Kallimachus was on the right hand side of the line, the position was seen as one of honour. In Sparta, that postion was left to the King or the highest ranking official in the army.
Kallimachus died at the battle, during the final push towards the Persian ships where most of the Greeks that were killed, died. It is not sure who took command of the forces after the battle, as there was still work to do in defence of the city, but probably Miltiades was the pseudo leader.
After the second Persian invasion into Greece, Miltiade's son, Kimon was in charge of the fleet of Athens and with the help of Aristides, gained the confidence of the outlying Greek cities, at first under the pretence of the Delian League, but shortly afterwards they became tributories of the Athenian Empire.
But during Kimon's command he weilded enormous power, and it has been suggested it was during this time that Kimon advanced the theory that his father was really the main catalyst behind the defence of Athens at Marathon. It may also have been at this time that Kimon gave a past helmet of Miltiades to Olympia, to help advance his fathers hero status, many assume that the helmet was giving straight after Marathon.
It may be that with Kimon's father, already dead from a wound in another battle, Kimon tried to advance his own military credentials by making is father the hero at Marathon. With Kallimachus dead, and Kimon weilding great power, the history of the battle may have been altered by time.
Artifact: Here is a picture of the top of the Monument to Kallimachus held by the French in the Louve Paris France.
Shortly after the Battle of Marathon, the so called 'Monument to Kallimachus' (also called the Nike of Kallimachos) was dedicated. The image is of a figure, marble with a necklace of bronze and perched atop a tall, inscribed ionic column, was represented as if descending from heaven to proclaim the news of the victory at Marathon. Lots of words on the base are missing and are variously restored, but one plausible reading of the inscription suggests that the dedication had a more complicated history than that:
Kallimarchos of Aphidnai dedicated me to Athena; the messenger of the immortals who have their homes on Olympus; since he was victorious as polemarch in the Athenian games; and at Marathon fighting bravely he won fairest fame; for the men of Athens, and a memorial of his own excellence.
the best interpretation is that Kallimachos, the Athenian polemarch or chief of staff in 490 B.C., had just won a contest at the Panathenaic Games before leading his forces to Marathon, where he fell on the beach as one of the 192 Athenian casulaties, and that the dedication, vowed before Marathon, was made posthumously in his name to honor both his athlectic and military victories.
This diagram was a reconstruction of the monument by M Korres. It shows the parts of the monument found and how it is believed they are pieced together.
*1 'Histories' by Herodotus (5.109)