Yueh Fei was a famous general in the South Song Dynasty.

When he served under a Field Marshal defending the enemy from the North, The Field Marshal went over to the enemy.

Disgusted, Yueh Fei resigned and returned home to care for his mother.

His mother was displeased, and lectured him that a soldier's first duty is loyalty to his country.

To be sure that the admonition will never be forgotten, she tattoo the words on his back!

Yueh Fei went back and led another army to defend the country.

The first word, from the left, means the most, the ultimate.
The second word means loyalty.
The third word means to serve.
The fourth word means country.