right-hand man
noun [ C usually singular ] uk/ˌraɪt.hænd ˈmæn/ us/ˌraɪt.hænd ˈmæn/
(尤指工作上的)得力助手,左膀右臂
someone who helps and supports you the most, especially at work
How will he cope without his right-hand man? 失去了得力助手,他如何应付呢?
Compare: girl Friday man Friday