A revolutionary is a person who either actively participates in, or advocates revolution. Also, when used as an adjective, the term revolutionary refers to something that has a major, sudden impact on society or on some aspect of human endeavor.
The term —both as a noun and adjective— is usually applied to the field of politics, and is occasionally used in the context of science, invention or art. In politics, a revolutionary is someone who supports abrupt, rapid, and drastic change, while a reformist is someone who supports more gradual and incremental change. A conservative is someone who opposes all such changes. A reactionary is someone who wants things to go back to the way they were before the change has happened.
Revolution and ideology 
According to sociologist James Chowning Davies, political revolutionaries may be classified in two ways:
- According to the goals of the revolution they propose. Usually, these goals are part of a certain ideology. In theory, each ideology could generate its own brand of revolutionaries. In practice, most political revolutionaries have been either anarchists, communists, democrats, fascists, liberals, libertarians, nationalists, republicans, or socialists.
- According to the methods they propose to use. This divides revolutionaries in two broad groups: Those who advocate a violent revolution, and those who are pacifists.
The Revolutionary is a doomed man. He has no private interests, no affairs, sentiments, ties, property nor even a name of his own. His entire being is devoured by one purpose, one thought, one passion—the revolution. Heart and soul, not merely by word but by deed, he has severed every link with the social order and with the entire civilized world; with the laws, good manners, conventions, and morality of that world. He is its merciless enemy...
Marxist revolutionary Che Guevara said this about revolutionaries: "At the risk of seeming ridiculous, let me say that the true revolutionary is guided by a great feeling of love.... We must strive every day so that this love of living humanity will be transformed into actual deeds, into acts that serve as examples, as a moving force."