This documentary about Ralph Nader achieves the remarkable effect of simultaneously making you admire its subject and think of him as rather obnoxious. Those who dismiss him as an arrogant kook should be led to reconsider in view of the undeniable service to the country “An Unreasonable Man” shows him to have done over the years. And those who revere him, and maybe voted for him in recent presidential elections, may be induced to reconsider whether or not he’s done more harm than good to the political process. By presenting both sides, even if unequally, the film manages to do something very like justice to an important if controversial figure.

The film by Henriette Mantel and Stephen Skrovan makes good use of archival footage and interviews—with past allies, critics, and Nader himself—to cover the activist’s life, beginning with his Connecticut boyhood (his father encouraged his children to “get involved”) through his Harvard Law days and his concern for a friend seriously injured in a car crash—which led him to become a crusader against poorly designed autos, his first great campaign. His book, “Unsafe at Any Speed,” not only made him a famous David bravely battling against corrupt corporate Goliaths (the largest of which—GM—was actually revealed to have hired investigators to dig up dirt with which to discredit him), but led to the formation of “Nader’s Raiders,” the college students who formed an army of volunteer investigators looking into all sorts of consumer-advocacy issues. Nader quickly became a political player during the Carter years, only to be disillusioned by the lack of progress, and was shut completely out of the loop when the Republican resurgence and the later “Clintonization” of the Democratic party seemed to halt it altogether and turn back the clock.

It was that disillusionment that ultimately led Nader to undertake his third-party presidential campaigns, for which some—even past allies—have come to consider him an egomaniacal spoiler. It’s interesting to watch Nader tilting against political windmills in his later years and justifying his actions, but it’s unquestionable that he’s tarnished his image among others who were formerly among his most ardent supporters. And they get their say, too.

“An Unreasonable Man” has been nicely edited to bring it down to a still- substantial two hours from the three-hour cut that was screened at Sundance last year. It passes smoothly, mixing in some moments of levity with its mostly serious approach, and provides a telling portrait of a man who sees himself as the champion of the little guy, and may just be right in his assessment.