Pablo Picasso's The Bull is a series of eleven lithographs created in 1945. It depicts the bull at various stages of abstraction, starting with a fairly realistic depiction and ending with nothing but a few lines.
The first lithograph in the series appears light and spontaneous, as if it were quickly sketched with a brush and ink. The features are fairly accurate and there is some rendering of shadows.
The bull then starts to transform into more of a mythical beast, with exaggerated horns and a robust appearance. The shadows are also dark and imposing.
By around half-way through the series, the bull starts to take on a more typical Picasso appearance, with abstract shapes and stylized features.
Picasso continues to simplify the form, straightening out the lines and flattening the planes.
The final lithograph is nothing but a simple line drawing to depict the bull.
Learning how to take complex subjects and simplify them down to abstract forms is a major aspect of art. Most people think that art is all about seeing more detail, but it is really about seeing less. Seeing basic patterns amongst the "noise"; seeing basic forms amongst the complex; seeing the few important details which convey the majority of meaning.
Picasso took it a step further by adding the mythical bull between the realistic and abstract depictions. This represents the exaggerated perception of the bull. Perception is what allows everyone to experience the world in a unique way and it is why art is so diverse.
(If you want to learn more about the principles of art, you might be interested in my Painting Academy course.)