Any short list of the most powerful jurists of the last half century would have to include Aharon Barak, former Chief Justice of the Supreme Court of Israel at or near the very top. In a legal system in which many had previously thought parliamentary supremacy the operative grundnorm, and with only the text of a handful of "basic laws," Barak established his court as a power to be reckoned with.
To be sure, Barak was never the activist countermajoritarian monster that his critics decried. For example, Judge Posner wrote a largely negative account of Barak in The New Republic, (which is only available in full text to TNR subscribers or via Lexis or Westlaw). In it, Posner said, among other things, that Barak has said that the Knesset cannot repeal the Basic Laws---a view that I do not think Barak has actually espoused. More broadly, Posner and fellow Barak critic Robert Bork (with whom Posner has his own methodological disagreements) seem unaware that Israeli judges in general are expected to be much more "activist" than U.S. judges. In contract law, for example, Israeli judges routinely infer/impose terms that are nowhere evident on the face of the contract. And further, despite his methodological activism, Barak's substantive rulings have, for the most part, been agreeable to the Israeli public and political classes (as Posner acknowledges).
Like any revolution built on the force of the leader's personality, it was unclear how much of Barak's legacy would survive his retirement from the Court last year. The most recent decision (reported in the NY Times here) requiring the rerouting of the West Bank security barrier/fence/wall illustrates that Barak's successor, Dorit Beinish, will continue to lead a powerful court. Beinish's substantive views are hardly surprising, given the role that Barak and his allies played in naming her as the new Chief Justice, but there was no guarantee that Beinish would be able to lead the court as effectively as Barak did. Barak, after all, had been called the "John Marshall of Israel," and like Marshall, he was able to produce results as much by force of personal charisma as by the force of his arguments. So far, it appears that Beinish will be able to do much the same.