Found object art, or art that incorporates already made materials, is a form of art that often elicits controversy over what "art" really is--while it began as a conscious technique early in the twentieth century, it continues on today. 

Readymades were everyday objects that were chosen and then adjusted by the artist before being put on display. Examples include Duchamp's own provocative "Fountain," which was simply a urinal. He saw this as a response to so-called "retinal art," or art that only affected its viewers through sight.

Jeff Koons is a controversial modern sculptor, as he has often turned his eye to pop culture subjects considered outside the realm of high art. Notably, he has a series called "Banality," and has constructed immense metallic sculptures of balloons twisted into animal shapes. While his subjects tend to be "lighter" compared to his contemporaries, like George Segal, Koons' skill with steel and his non-traditional subjects have been highly influential on younger generations of artists, including Damien Hirst and Mike Leavitt.

Duchamp is responsible for this three-dimensional art piece. The piece was signed "R. Mutt," but the origin of this signature is still debated, though it is said to stand for Richard Mutt.

Christo and Jeanne-Claude's installation art piece The Gates was set up in 2005.

Image accessed through Wikipedia Media Commons: https://en.wikipedia.org/wiki/The_Gates#/media/File:Gates_a.jpg

Dan Flavin's fluorescent light tube sculptures used the objects' eerie glow to give the area around them an unusual energy. Marcel Duchamp is famous for his urinal readymade "Fountain," while Jeff Koons employed vacuums in his early work. Dali created a Lobster Telephone, and trash art is a genre unto itself.

"A Subtlety" was housed in an old sugar plant and depicted a slave woman naked except for a headscarf in the pose of a Sphinx. The sculpture fused ancient art with the abuses of American slavery in a massive sculpture.

Claes Oldenburg is best known for Pop Art sculptures of everyday objects and more specifically his "soft sculptures". His soft sculptures consisted of creating large, everyday objects so they collapse like a deflating balloon.

The Italian Renaissance began in the city-states of Northern Italy, which were ruled over by no king, as a larger project of enhancing their authority. The David was made by Michelangelo to fulfill a contract with the Overseers of the Office of Works of the Duomo, which was the cathedral of Florence. The David's subtle turn, wary glare, and perfect form helped the stature to become a symbol for Florence.

Beginning in 1914 and continuing until his death in 1968, the French artist Marcel Duchamp created sculptures he termed "readymades." Duchamp took essentially everyday objects and mounted them as sculptural pieces in galleries. The pieces grew to be less found objects and more objects built to look like common items, often presented with absurd or humorous titles.