祸首

tā shì zuó tiān nà chǎng dòu zhēng de huò shǒu

他是昨天那场斗争的祸首。

He was the one who instigated yesterday's brawl.

zuì kuí huò shǒu

罪魁祸首

arch criminal

zhǎo dào le fā bìng de huò shǒu biàn kě yǐ duì zhèng xià yào

找到了发病的祸首，便可以对症下药。

Found the incidence of the culprit, we can prescribe the right medicine.