There are several legends behind this statue, but the most famous is the one about Duke Godfried II of Brabant. In 1142, the troops of this two-year-old lord were battling against the troops of the Berthouts, the lords of Grimbergen, in Ransbeke (currently Neder-over-Heembeek). The troops put the little boy in a basket and hung it in a tree, to encourage them. From there, he urinated on the troops of the Berthouts, who eventually lost the battle.
Another legend goes like this: in the 14th century, Brussels was under siege by a foreign power (which?). The city had held their ground for quite some time. The attackers had thought of a plan to place explosive charges (where?). A little boy named Juliaanske from Brussels happened to be spying on them as they were preparing. He urinated on the burning fuse and thus saved the city.
There was already a similar statue made of stone in the middle of the 15th century, perhaps as early as 1388. The statue was stolen several times. In 1619 it was replaced by a bronze statue, created by Franco-Flemish Baroque sculptor Francois Duquesnoy.
On special occasions the statue is dressed in a costume. His wardrobe now consists of several hundreds of different costumes. According to an article posted in the History section of http://www.manneken-pis.com, the statue once was used to dispense liquor.
Photos of the statue in close-up often give a false impression of its size; some tourists are disappointed to find it much smaller than expected.
In the United States, replicas in brass or fiberglass are commonplace swimming- or garden-pool decorations. However, in September 2002 a Belgian waffle-maker Assayag set up a replica in front of his waffle stand in the Fashion Square Mall at Orlando, Florida. The Belgian owner recalled the legend as 'the boy who saved Brussels from fire by extinguishing it with his urine' (confusing the legend with an incident in 'Gulliver's Travels' perhaps). Americans are more used to seeing a version of 'Mannekenpis' adapted as a corkscrew, locally considered most risqué [1]. Consequently Florida's shoppers made a formal complaint. Mall officials said that the waffle-shop owner Assayag did not follow procedures when he put up the statue and was in violation of his lease.