A mensch is a gentleman, a "fine person." But that doesn't quite capture the feeling of "He's a real mensch!" The essence of being a mensch is to have a global perspective, to be somewhat introspective and philosophical, and to be kind. A mensch is good at listening and very good at seeing the other person's point of view.
We should remark here that the word mensch in German means human, and secondarily, man. While that makes this phase of life accessible to both genders, it is much more inclusive than the Yiddish usage. In Yiddish, not all humans are mensches.
There's a big difference between machers and mensches. First, machers usually have a very hard edge to them; mensches are mellower, softer, and more patient. Machers have a sense of urgency; mensches have a sense of inevitability. The mensch really believes that it all comes out in the wash. The schlepper is often viewed as dull or stupid, when in fact all he may be guilty of is ignorance; the macher is viewed as being smart or clever; the mensch is always viewed as being wise. You go to the macher when you want a problem solved now; you go to the mensch when you are looking for a long-term solution. In some sense, the schlepper can't do anything, the macher is the tactician par excellence, and the mensch is the strategist.
Before I let you think that the mensch is just a Yiddish incarnation of Yoda, I should point out that the mensch is not just a dispenser of advice, but also a doer of deeds. The thing that sets the mensch apart is that he not only knows the right thing to do, but he acts on it, even at great personal cost. Unlike the macher, the mensch is not at all interested in getting the credit for the result. He is vitally interested in the result for its own sake and doesn't really care if anyone ever knows he was the facilitator. A typical mensch-like thing to do is to make a large, anonymous donation to charity, for example.
Machers sometimes make good mentors, but only as an almost accidental side effect of their primary objective, which is to get results. Machers more often mentor more junior machers, as opposed to schleppers. Mensches, on the other hand, make superb coaches and mentors, because they are so highly attuned to the needs of others; they help everyone because they empathize with everyone. They also have a quintessential long-term perspective, so they understand the leverage of developing others and building infrastructure. They understand the Zen-like beauty of injecting energy into the system, unaware of when or where the positive consequences of that act will appearyet confident that they certainly will.
The mensch also provides a lot of lubrication in any organization. He's above the fray, committed to the organization and its goals, but without a personal agenda, unlike the macher, who always has one. The macher is territorial, whereas the mensch is extraterritorial. The mensch will endeavor to be a peacemaker, a mediator, and someone who is creative in trying to find a solution when there appears to be none. Appearances notwithstanding, the mensch is a highly effective person. His strength comes from his ability to work well with everyone and from the respect everyone has for him.
Can you become a mensch without having been a macher? There are two points of view.
The first is that the schlepper-to-mensch transition is sort of like going from apprentice to master craftsman without ever having been a competent journeyman in between. In this point of view, the wisdom the mensch exhibits is accumulated from years of being a macher; the really good machers age well and eventually become mensches.
The problem with this point of view is that there seem to be some clear exceptions. Just as we have noted that many machers never graduate to menschhood, it is also the case that we find a few people displaying the characteristics of mensches who have not been machers. They have schlepped for extended periods of time but have not become bitter. They have accumulated wisdom, are kind, and are secure in themselves. They universally understand people and the human drama, and they exhibit lots of empathy. Their judgment is impeccable. The mystery is where their wisdom came from.