Not "someone working 20 hours a day", but someone with enough dedication, discipline, and experience to work 20 hours a day sometimes because the workload is massive, and the pay is good (I'm assuming), and they do it well enough that people request their assistance consistently, and the word about the quality of their work spreads around.

This is what I meant. Someone who takes a job that others may not view as "high-class" and just does a great job, is reliable, and people like them for it.