upstart; parvenu; nouveau riche
Derogatory term for someone who has suddenly risen in status or wealth, often implying lack of refinement or proper background. Commonly used as a noun.
He is talked about behind his back as an upstart.
成り上がりの政治家は古い家柄の議員から軽蔑されがちだ。
Upstart politicians tend to be looked down on by lawmakers from old families.