Escherichia Coli (commonly abbreviated as E. Coli) is perhaps the most well-known of all bacteria, ever.
E.Coli is a rod-shaped, gram-negative bacteria, and one of the simplest life-forms to exist (and even then, it isn't exactly simple.)
It is a mostly harmless, if not helpful, bacteria, and its main biological function in humans is to aid the digestive system. Some species can infect and harm humans, causing diseases such as pneumonia, and stomach infections.
The harmful strains are found in undercooked meat and food similar to that.