Pheidon the King of Argos
NOTE TO DATING:
It should be noted here that all dates are approximate and have never been fully agreed to. Different scholars indicate different dates for events, such as the Pisatan revolt against the Eleians, ancient historians have given varing dates, from 672, 660 and 644 B.C. We are assuming (as well as many of today's scholars) that Pheidon was responsible for the victory at the Battle of Hysiae. It has never been written by ancient scholars that he was there or even alive at the time, but with what was happening before and after it seems very likely he was responsible.
Also, his story and timeline is entangled with the following events:
-The destruction of Assyria by the Medes and the beginning of the Median hegemony
-The founding of the Argead dynasty in Macedonia by Karanos, the brother (or son?) or Pheidon
-The Messenian Wars
-Lykourgos the lawgiver at Sparta
-The founding of Syracuse, which may have something to do with the conflict in Corinth to oust the kingship and to which Pheidon is believed to have meddled with.
So, even a slight error in dating ends up throwing off the whole timeline. What you should read here should be treated as a guide only, as books and other web sites you read will not totally agree with what you read here.
Pheidon was King of Argos, and a central figure in early Greek history, a fragment of Parian marble confirms him a noble and eleventh in descent from the demigod Herakles. The dating of his existance cannot be precisly proven, even in antiquity there was no agreement on this point. However, in his time, the definition of king no longer carried with it the power that it once held, his primary role was that of chief or high priest and often the arbiter in disputes. The real power in Argos was held by the nobles who also controlled a lot of land.
It seems that what is likely to have happend in Argos, was that at first there might have been an attempt on King Pheidon's life, either real or he might have organised the attempt himself. Eitherway, because of the attempt he received bodyguards and with an armed body for him to order, he quickly overthrew the ruling nobility, and proclaimed himself tyrant.  Which would explain the curious remake that Pheidon became tyrant from being king.
Aristotle, in "Politics", claims that he made changes to land reforms “family plots and the number of citizens should be kept equal, even if the citizens had all started with plots of unequal size.” It seems reasonable that with the help of the poorer pre-Dorian population, Pheidon was able to overthrow the nobles and solidify himself as tyrant of Argos, by weakening their hold over the land. 
Fearing retaliation from the once powerful nobels the bodyguard force that was first issued for his protection evolved in the first type of phalanx formation. The bodyguards tightly packing themselves around Pheidon, interlinking their shields and forming a wall of men to deter any citizen of Argos from attempting a assasination attempt on Pheidon..
Pheidon then gradually regained sway over the various cities of the Argive confederacy, the members of which had become practically independent, and (in the words of Ephorus) reunited the broken fragments of the inheritance of Temenus. His object was to secure predominance for Argos in the north of Peloponnese.
Having extended the influence of Argo's power around his city and finding himself the pre-Dorian element's champion, he was either pursuaded by that pre-Dorian element or saw the advantages of helping the pre-Dorian people of the nearby state of Elis.
The people of Elis like Argos consisted of a Dorian and a pre-Dorian element known as the Pisatans, who were the original inhabitants of the land. But unlike Argos, the Dorian element didn't just hold the upper hand by controlling the land around Elis it was a privileged body; they alone provided the presiding officers for the Olympic festival in the classical period, and they were doubtless descended from those who had conquered the land in the age of migrations. Sources such as Strabo, Pausanias and Eusebius say that the Dorian Eleans controlled the Olympic festival from it's inseption, which supposedly was 776 B.C.
It seems around 670 B.C, the Eleians were occupied in a war against there neighbours from Dyme, it may be because of Pisatans elements there, and as it has been suggested that a long drawn out Pisatan revolt was underway before Pheidon interludes. Pheidon used that oppotunity to forcibly interrupted the Eleian domination of the area. He invaded the district and celebrated the games himself, taking advantage of the fact that, because of their pre-occupation with Dyme and being in a sacred place, the Eleans did not have any arms with which to defend themselves. Soon after Pheidon took over the nearby sites of Pisatis and Triphylia also in Elis. This movement expanded Pheidon's influence towards the state of Messinia, which was currently under the sway of Sparta. We can assume (though it has not been documented) that this provided an oppotunity for citizens of Messenia to head towards Elis, away from the influence of Sparta and under the more understanding control of Pheidon.
Regardless, the expanding Argos dominion threatened Spartas influnce in the Peloponnese. The Spartan military machine marched out towards Argos, but cleverly Pheidon took his forces away fom Argos and holed them up in the city of Hysiae, the next major town away from Argos towards Sparta. This is clearly a military objective as it was usual for armed forces to met in the open plains to best use their forces in wide spaces.
The ensuing battle is called the Battle of Hysiae and resulted in a clear victory to Argos. Pheidon may have used the city's streets to advantage to funnel in the advacing Spartan forces and probably using his bodyguards in the first ever proto-type phalanx formation. The Spartans ran headlong into the tightly packed Argos phalanx and there perished.
Pheidon is credited with the first weights and measures in Greece. It is generally agreed that a system was already in existence in the time of Pheidon, into which he introduced certain changes. A passage in the Aristotelian Constitution of Athens states that the measures used before the Solonian period of reform were called Pheidonian. He mentions "a peidon would be a jar of olive oil, named from the Pheidonian measurements." It is mentioned that Solon reforms these measurements from the 70 drachmae of the Pheidonian coins to the 100 drachamae coins.
Pheidon throughout his reign seems to have been meddling in Corinthian affairs. At Corinth, the kingship was being challenged by relatives, it is not certain who's position Pheidon was siding with. But at one stage Plutarch, says Pheidon attempted to break the power of Corinth, by requesting the Corinthians to send him 1,000 of their picked youths, ostensibly to aid him in war, his real intention being to put them to death; but the plot was revealed. During some interlude that is not quite clear, Pheidon perished while trying to help one of the fighting factions in the strife that led to the abolishment of the Corinthian kingship and the establishment of the Bakchiad oligarchy in Cornith.
The ancients  would later contrast an up and coming prosperous Sparta with the decline of other states in the Peloponnese, namely Messenian and the weakening of the previously dominate Argos. The Spartan lawgiver Lykourgos and Pheidon must have been crucial figures in the process, the first as the wise and virtuous architect of Sparta's laws and the second as the king whose excessive ambitions led to sacrilegious acts and the downfall of his previous hegemony. Plato, was quite explicit about the tyrannical behaviour of the Messenian and Argive kings, being the cause of the decline of these states, while pointing out that similar developments in Sparta was checked by Lykourgos. 
Politics by Aristotle 5.1310b 26-28)
H 6.127 His son as suitor
Aristotle Pol. 5.1310b
According to both Nikolaos of Damascus FGrH 90 F 35. And Ephoros
Isokarates, Plato and Ephoros as well.
Plato, Nom. 690d-692b