Ophir was a region known for its wealth and precious materials, especially gold. In the Old Testament, Ophir is frequently referred to on account of its gold using the phrase "gold of Ophir"; meaning precious gold. In the Books of Kings and Chronicles there are several historical references of the kings Solomon, Jehoshaphat and Hiram trading with Ophir. Asides from its gold, special references are made to its silver and to almug wood (which are noted for its fine quality)
Ophir was known for its gold from a very early period in history. The fact that it is not only mentioned by Job and Eliphaz, but is used as an expression for precious gold, shows that is was well known by the rest of the world for quite some time. Since Job's life occurred early in the post-diluvian period, Ophir had significant trade interactions with Levantine society for its reputation to develop. It was known for its gold long enough before the time of Job's suffering, that an idiom developed that was dependent upon common knowledge of Ophir's abundance of gold.
David had acquired at least three-thousand talents of gold from Ophir during his reign. During an offering ceremony for the planned Temple, David pledged three-thousand talents of Ophir's gold for the future construction of the Temple, under the stewardship of Solomon. 
During the reign of Solomon, Solomon contracted the King Hiram of Tyre's seafarers to bring materials from Ophir. They brought four-hundred and fifty talents of gold as well as silver and unique wood (almug, which is noted for its high quality, for there "was nothing ever like it before" in the land). The gold and silver were used in his two major building projects: his personal palace and the Temple of God. The almug wood was used as structural support in both projects and in instruments for Solomon's singers.
Jehoshaphat's Failed Trade
Jehoshaphat, the king of Judah attempted to obtain gold from Ophir during his reign. However, his trade fleet sent from Tarshish was shipwrecked at Ezion-Geber so they were not able to travel there. When Ahaziah, King of Israel, offered to conduct a joint expedition with Judah, Jehoshaphat refused. Jehoshaphat had created an alliance with Ahaziah and they built a fleet, which God considered wicked; therefore God allowed the ships to be wrecked. So he heeded the warning and decided not to sail with Israel. 
In the midst of Job's suffering, three of his friends: Eliphaz, Bildad and Zophar tried to offer comfort through their wisdom. While their speeches contained many wise insights, they have a fundamentally wrong understanding of God's justice- saying that if Job were suffering, God must be punishing him for a sin.
Eliphaz suggested that perhaps Job was not caring for the needy with his (formerly) great wealth. Therefore, Eliphaz exhorted Job that if he were to abandon his gold to dust and the gold of Ophir to gorges, then he could treasure God and would be in a right relationship with him. Eliphaz rightfully stated that if someone (Job) considered their possessions worthless and elevated God higher, they would have a relationship with God. Eliphaz's reference to "the gold of Ophir" as a valuable possession shows a culturally significant recongition of Ophir's wealth in the ancient near east.
Wisdom More Valuable than Gold
In Job's response to his friends accusations he considered the search for wisdom. Job recognized that wisdom could not be mined as precious metal in the deep pits of the Earth. He declared that the value of Ophir's gold could not be compared to the value of wisdom; again showing a widespread understanding of Ophir's gold being of high value.
A Queen Dressed in Gold
The 45th Psalm was a Maskil love song written by the Sons of Korah to the tune of Lilies. In this psalm, the psalmist described the splendor and majesty of a certain king, called an elohim (or even God himself). The psalmist described the queen clothed in the gold of Ophir.
In his praise of the elohim, the author described his Queen in detail. The queen is described as sitting at the elohim's right hand, clothed in the gold of Ophir. Further on, this elaborated when this psalmist describes her robes being interwoven with gold. The description of the queen occupies half of the psalm and is important to the praise of the elohim. Since the queen belongs to the elohim king, the queen being dressed in robes of Ophir's gold indicate the king's power. This is not only a symbol of the worth of the queen herself, but the king's possession of the queen's value.
Through the prophet Isaiah, God spoke for Babylon. The judgement stated that God would make the people of Babylon rarer than the gold of ophir, a hyperbolic way of saying the Babylonian would become exceedingly rare--or the the population would be dramatically reduced.
The present location of Ophir is unknown, but multiple locations have been suggested by various scholars.
A pottery shard was discovered at Tell Qasile, which bore an inscription referencing thirty shekels of Ophir's gold designated for Beth-Horon.