Some future historian may well title the saga of building a newFenway Park, ``Machiavelli Meets Martinez.'' But as the tale winds down, a most un-Machiavellian man may shape its conclusion: Sam Tyler.

Niccolo Machiavelli was the Renaissance-era nobleman whose rules of politics (to wit, ``whoever is the cause of another becoming powerful, is ruined himself'') spoke to the crafty accumulation and use of power.

But Machiavelli would never have been able to figure out Tyler. Arguably one of the most powerful people in Boston, Tyler got that way not through scheming or patronage but instead through careful research, an insistence on accuracy and unrelenting honesty.

Tyler heads up the Boston Municipal Research Bureau.

Intending it to serve as a watchdog on city finances, business groups created the bureau in 1932, during the mayoral reign of James Michael Curley. Curley hated the organization, calling it ``a selfish band of raiders masquerading under a most imposing title.'' Back then, such barbs hurt. Today, and particularly coming from a man such as Curley, they are a compliment.

Mayors since Curley generally adopted a less contentious posture with the bureau. John Hynes, John Collins and Kevin White all relied on the bureau to help the city tighten up its financial affairs and to help make Boston a more attractive place in which to do business.

But Tyler, who became director in 1983, moved the bureau to a different plane. Where once the organization was business' gimlet eye on messy city finances, Tyler remade the bureau into a voice independent of business, independent of anything except a considered notion of the public good.

It is a voice of real power. The bureau helped to select the Rouse Co. to redevelop Quincy Market. The organization was instrumental in shepherding through financial reforms in the early years of the Flynn administration, called the Trager reforms, which put Boston's fiscal house in order.

In 1978 the bureau undertook to restructure the Boston school department. It was a long-term effort that culminated in 1996 by making the School Committee appointed rather than elected. Tyler-led analyses of the soon-to-be-built convention center and the merger of Boston City Hospital into the Boston University Medical Center were critical to making those events happen.

Editorial writers at both Boston dailies rely upon Tyler. And although he regularly assists city councilors and mayors, he just as regularly infuriates them. He is frequently denounced from the floor of the council chamber, particularly when he skewers some hare-brained scheme or questions the latest round of salary increases for council members.

Tyler himself is a curiosity. As he notes, ``the bureau is my life.'' Today, at 53 years old, he looks little different from when, at age 25, he first joined the bureau as a research associate. He is boyishly handsome, replete with short blond hair cut boy's-regular style.

Tyler lives in Holliston. ``I've never bought into this residency nonsense,'' he says. He has been married for 30 years and has three children. He works yeoman's hours, coming to work at 7:30 a.m. and rarely leaving before 6 p.m.

Why does he do it? It certainly isn't the trappings. The bureau is housed in a 1,000-square foot suite of offices in a downtown building that, at best, could be described as ``dumpy.'' With a total budget of just $450,000 and a staff of five, the organization generally provokes the reaction of, ``This is it?'' from first-time visitors.

``I enjoy government. I enjoy seeing the bureau make a difference,'' allows the self-effacing Tyler. In truth, Tyler is one of those most  rare, and therefore remarkable, men: a true public servant. He labors neither for money nor glory (and gets little of either), but instead for the satisfaction of improving public policy.

Last week, eight Boston city councilors made public a letter correctly questioning whether it was in the financial interests of the city to put up money to help build a new Fenway Park.

Tyler shares those concerns. He is skeptical of efforts by municipalities to spend public money to aid private businesses. When it comes to the Red Sox, Tyler's questions are, ``Is it good forBoston? What is the cost vs. the benefit?''

The great success of Tyler's work is that Boston is financially stable, in large part because Tyler and the bureau have forced the city, from a fiscal point of view, to behave responsibly. That success is reflected in Boston's ``AA'' bond rating. Boston is in the position to deliver basic city and social services it otherwise would be incapable of paying for.

It's a success that Tyler won't jeopardize. When it comes to the Red Sox, almost everyone will have an agenda. Money, prestige and political power will all be at stake. Tyler will have an agenda as well but it will be the public's, not his own.

By dint of his years at the bureau and his reputation for dispassionate analysis, Tyler has extraordinary credibility. It is the source of his power.

Thus a prediction. If and when a deal is struck with the Red Sox, all eyes will turn to Sam Tyler. And if Tyler doesn't sign off, it won't happen.

Tom Keane writes regularly for the Herald. He can be reached at tomkeane@tomkeane.com.