A Fascist (a noun word) is a person who practices the political system called fascism and in other to understand better I'll explain the it's verb "fascism". Fascism is a system of government headed by a dictator, depriving people of chances to vye or content for power. A fascist system is authoritarian in nature with the absence of human right and party system. So when you asked for who a fascist is, fascist is a person being anti-democratic in nature and believes that people deserves to be in the hands of a dictator.
For example we can say someone like Benito Mussolini is a fascist because clearly he was the originator of fascism and believes that government without competition but concentrated in the hands of a singular dictator will create a perfect socio-economic system by all means.
So in simplicity now that I've made you understood what a fascism is, it's now easier to understand other than just knowing that a fascist is a person who believes practices and operates Fascism as the best system of government, you also now know what Fascism is
(1) Politics. someone who supports fascism..
(2) Politics a person of the far right in politics..
(3) Disapproving someone who does not allow any opposition...
(Eg) He thinks all policemen are fascists and bullies.