老黄牛

Traditional (Taiwan): 老黃牛

lǎohuángniú ㄌㄠˇ ㄏㄨㄤˊ ㄋㄧㄡˊ

    • person who works hard and conscientiously without seeking reward or credit

Character by character

Saying俗语俗語

Idiom惯用语 · In everyday use

Literally
old ox
Meaning
A person who works hard and conscientiously, without thought of reward or credit. Approving.

Sources