Happy Merchant is a highly offensive caricature depiction of a Jewish trader, or merchant, as he is rubbing his hands in anticipation.
The portrayal is offensive, due to the heavy stereotypical and anti-semitic depicition elements in it, like a big nose, greed, manipulative tendency and of course megalomania.
It is most seen on the /pol/ thread of 4chan either in an ironic or a serious manner.
Origin of the meme
The original drawing was created by an artist, who took on the pseudonym of A. Wyatt Mann.
The portrayal was part of a racist image, where the creator is making the statement, that living in a world without Jews and black people, would be like living in a world without rats and cockroaches.
The drawing was then cut out of its original context and uploaded to the /new/ thread of 4chan.
Spread of the meme
The Happy Merchant was then used in memes and threads on 4chan, mainly centered on Jewish conspiracies about ruling the world and oppressing hard working people.
While some users used it in an ironic and satirical manner, there are those people, who found their opinion reflected in the portrayal of Jews in this way, so it is often seen in serious posts as well.
The drawing had since turned into a reaction image.