Who is Overseas Chinese Lu from Death of a Red Heroine and what is their importance?

Overseas Chinese Lu is one of Chen's oldest friends. Chen loans Lu money to open a restaurant and uses his connections to help him wherever he can. Lu also provides a safety net of sorts for Chen when he considers quitting the police force, as Chen's interest in the restaurant provides him with a job to fall back on if he finds his career in ruins. Chen is described as exuberant and outgoing.