An anion is a monoatomic or polyatomic species having one or more elementary charges of the electron.
The English scientist Michael Faraday discovered the anion in 1834 while analysing the electrochemical properties of electrolytic solutions. In an effort to create an electrochemical nomenclature, he says in his 1834 publication, “Finally, I require a term to express those bodies which can pass to the electrodes, or, as they are usually called , the poles. Substances are frequently spoken of as being electro-negative, or electro-positive, according as they go under the supposed influence of a direct attraction to the positive or negative pole. I propose to distinguish such bodies by calling those anions which go to the anode of the decomposing body; and those passing to the cathode, cations; and when I have occasion to speak of these together, I shall call them ions. Thus,the chloride of lead is an electrolyte, and when electrolyzed evolves the two ions, chlorine and lead, the former being an anion,and the latter a cation.”
Here is an oil painting of Michael Faraday: