right-hand man; trusted henchman
Literary term for a highly trusted subordinate or close aide, often in political or organizational contexts. Conveys deep reliance, similar to 'right-hand man'.
He has supported the company as the president's right-hand man.
The general gathered his trusted retainers and devised a strategy.
From Chinese 股肱 (gǔgōng), literally 'thighs and upper arms', metaphorically referring to essential limbs of a ruler, i.e., indispensable aides. The Japanese reading is on'yomi.