What does The Equalizer do for a living?

I'm curious, can you tell me more about The Equalizer's occupation? What exactly does he do to make a living? Is it a high-risk, high-reward type of job, or something more stable and predictable? It seems like he has a lot of resources and expertise, so I'm guessing he's involved in something fairly sophisticated. Can you elaborate on his line of work and how it allows him to carry out his various missions and endeavors?