Sumerian merchant, dates of birth and death unknown, but living in approximately 1750 BCE in the city-state of Ur. (His name is more accurately spelled Ea-nāṣir in English, but that non-standard "a" and "s" would play hell with searching on E2, so I ain't gonna do it.) We know almost nothing about him (but see Clockmaker's writeup for more), aside from his occupation -- copper merchant -- and his reputation among his customers -- really, really not great.
The only reason we even know his name is from a complaint letter, sent on a clay tablet, from a customer named Nanni. The tablet says that Ea-nāṣir had traveled to Dilmun (now encompassing eastern Saudi Arabia, Kuwait, and Bahrain) to buy copper to sell in Mesopotamia. He had agreed to sell some copper ingots to Nanni, who sent a servant to pay for the copper and bring it back home. When he received the shipment, Nanni refused to accept the copper and sent the complaint letter, saying the copper was the wrong grade. He also said his servant had been treated rudely, and that Nanni had paid money for copper that he had not accepted.
Here's the translated text of the tablet, broken into paragraphs to make it a bit less of a wall-of-text:
Tell Ea-nāṣir: Nanni sends the following message: When you came, you said to me as follows: "I will give Gimil-Sin (when he comes) fine quality copper ingots." You left then but you did not do what you promised me. You put ingots which were not good before my messenger (Sit-Sin) and said: "If you want to take them, take them; if you do not want to take them, go away!"
What do you take me for, that you treat somebody like me with such contempt? I have sent as messengers gentlemen like ourselves to collect the bag with my money (deposited with you) but you have treated me with contempt by sending them back to me empty-handed several times, and that through enemy territory.
Is there anyone among the merchants who trade with Telmun who has treated me in this way? You alone treat my messenger with contempt! On account of that one (trifling) mina of silver which I owe you, you feel free to speak in such a way, while I have given to the palace on your behalf 1,080 pounds of copper, and Šumi-abum has likewise given 1,080 pounds of copper, apart from what we both have had written on a sealed tablet to be kept in the temple of Shamash.
How have you treated me for that copper? You have withheld my money bag from me in enemy territory; it is now up to you to restore (my money) to me in full. Take cognizance that (from now on) I will not accept here any copper from you that is not of fine quality. I shall (from now on) select and take the ingots individually in my own yard, and I shall exercise against you my right of rejection because you have treated me with contempt.
And it's not the only example of Ea-nāṣir's low skills as a merchant. Other tablets found in his dwelling were a letter from someone complaining that he hadn't gotten the copper he ordered yet, and another complaining about all the bad copper he had to pay for. It seems likely that Ea-nāṣir was just a lousy businessman selling bad copper for too much money and being rude to everyone besides.
Physically, the tablet is about four and a half inches high, two inches wide, and an inch thick. It's slightly damaged, which ain't bad for a clay tablet almost 3,800 years old. The letter is written in Akkadian cuneiform. It was acquired by Sir Leonard Woolley during a joint expedition by the University of Pennsylvania and the British Museum from 1922 to 1934. It's currently being held by the British Museum among its vast collection of stuff they've stolen from other parts of the world.
Why is Ea-nāṣir important to us today? Partly, it's because he's a historical curiosity -- the letter has been recognized by the Guinness Book of World Records as the Oldest Customer Complaint. But he and the letter have also been extensively meme-ified. It is funny to see that there have been crooked, rude businessmen all through the ages and in every other culture, and that turned it into something that Tumblr loved to make jokes about. So anything having to do with bad businesspeople gets an Ea-nāṣir meme. Anything having to do with copper gets an Ea-nāṣir meme. Anything having to do with clay tablets gets an Ea-nāṣir meme. Anything having to do with ancient history, especially ancient Mesopotamian history, gets an Ea-nāṣir meme.
And they still end up being relevant and at least a little funny. Because there are so many terrible people running businesses, even after 3,800 years. And the only way to revenge ourselves on these greedy assholes -- legally -- is to laugh at their expense.
Research:
Wikipedia
Really Shitty Copper subreddit