在英文中，"he became very dangerous" 或 "he became a danger" 可以表示 "他变得非常危险"。
这句话的来源可能是你想描述一个人变得更加危险或有潜在危险性。这句话的意思是，这个人以前不是很危险，但是现在变得危险了。
下面是一些英文例句和中文翻译：
He became very dangerous after he started using drugs. 他开始吸毒后变得非常危险。
The situation became dangerous when the crowd started to get violent. 当人群开始暴力时，情况变得危险。
The weather became dangerous when the storm hit. 暴风雨来临时，天气变得危险。