The origins of this period of judicial activism went back to the 1930s, when Brennan was still practising law in his native New Jersey. Facing the crisis of the great depression, when one American in four was unemployed, Congress passed emergency legislation which the conservative Supreme Court struck down as unconstitutional. Though Congress rejected President Franklin Roosevelt's attempt to reform the Court, the death of its older and more conservative justices enabled Roosevelt to appoint liberal successors.
These justices, like Hugo Black, Felix Frankfurter and William 0. Douglas, were the core of the Court when Eisenhower appointed Earl Warren and Brennan himself in the 1950s. Eisenhower came to regard the appointments as among his worst mistakes, but Brennan had given public warning of his views.
He had defended the rights of criminal defendants in speeches in his home state of New Jersey, attacked President Truman's use of loyalty oaths and compared the excesses of Senator Joe McCarthy to the Salem witch trials. McCarthy cast the lone dissenting vote when the Senate confirmed Brennan's appointment.
He was born in 1906, the second of eight children, to a father who was a coal shoveller in a local brewery before becoming a prominent labour leader and municipal reformer. William, who graduated near the top of his class at Harvard Law School, believed the Court should give the Constitution a broad construction promoting individual liberty and equality.
The stage was thus set for the most astonishing period of judicial activism in American history. Eisenhower was a passive president. Congress, riven by conservative/liberal and many other factions, was unable to act. Yet the times demanded action, and the Court moved to provide it.
The field demanding action most urgently was civil rights, and it was here, in Brown v Board of Education (1954), that the Court overturned centuries of racial segregation and began a generation of black struggle by declaring segregated schools unconstitutional.
Southern resistance was widespread. "We are under a Constitution," Chief Justice Hughes had said in the 1930s, "but the Constitution is what the Supreme Court says it is". This essentially conservative doctrine was now used by liberals to justify reform. But perhaps liberal and conservative ideology is the wrong way to look at the problem. Brennan believed the Constitution embodied "a sparkling vision of the supremacy of the human dignity of every individual" and that its "genius rests not in any static meaning it might have had in a world dead and gone, but in the adaptability of its great principles to cope with current problems and current needs."
This doctrine of the flexible Constitution ran through all the Court's momentous decisions Brennan played such a decisive part in shaping.
Brennan also helped tackle the problem of enforcement. Despite his junior rank, he wrote the forceful majority opinion in Cooper v Aaron (1958) which restated the doctrine of federal judicial supremacy to overturn the South's "massive resistance" to desegregation orders.
From now on his position became pivotal. His superb personal, tactical and intellectual abilities made him the ideal "coalition builder" on the Court. Chief Justice Warren said of Brennan that, "Friendly and buoyant in spirit, a prodigious worker and a master craftsman, he is a unifying influence on the bench and in the conference room." He became Warren's closest colleague and the two met weekly before court conferences to discuss cases and plan strategy.
His majority opinion in Baker v Carr (1962) was most significant. It went to the heart of conservative resistance to change. For generations, rural areas had been greatly over-repesented in Congress. It took far more urban than rural votes to send one Congressman to Washington. Moreover, since Democrats monopolised Southern politics, their seniority gave them control of crucial Congressional committees.
The reapportionment revolution Brennan began changed all that in the 1960s and 1970s by enforcing the rule of "one man one vote". Warren later described the decision as the most important of his tenure.
But Brennan was equally concerned with the rights of women. His theory of an evolving Constitution underpinned his efforts to curb government attempts to curb individual "privacy" - a word nowhere mentioned in the Constitution. By such reasoning in Einstadt v Baird (1972), he struck down a state law making it a crime to sell contraceptives to unmarried women.
The culmination of his thinking came the following year in his epoch- making opinion in Roe v Wade, which legalised abortion. Finally, in Craig v Boren (1976) he became the Court's most vocal advocate of gender equality, openly supporting the proposed Equal Rights Amendment.
Justice Brennan played a similarly forceful role in such fields as affirmative action to end racial discrimination, expansion of habeas corpus and other judicial remedies for denial of liberty, freedom of speech and the acceptance of welfare rights as "property" hallowed by the law.
Placed so squarely at the centre of the Warren Court, Brennan was the justice least likely to dissent. When he did, he attacked the barbarity of the death penalty, its arbitrary nature, and its disproportionate use against minorities, youth and the retarded, to such effect that he almost succeeed, in the 1970s, in converting the Court to his view that capital punishment was "a cruel and unusual punishment" prohibited by the Constitution.
But by then the nation's mood was changing. Liberalism was being replaced by a new conservatism, personified in William Rehnquist's apppointment as chief justice. The Constitution was being re- interpreted again in light of changing times, but right to the end Brennan fought his corner. In 1990 - the year he retired from the Court - in a decision invalidating laws making it a crime to desecrate the flag, he wrote, "We do not consecrate the flag by punishing its desecration, for in doing so we dilute the freedom that this cherished emblem represents."
Brennan's critics claim he epitomised that unrestrained federal judiciary that arrogated to itself ultimate control over almost every aspect of daily life. His view of America as a secular democracy and opposition to prayer in public schools made them especially angry. But Brennan rebutted their arguments as "little more than arrogance cloaked as humility".
William Joseph Brennan, judge: born Newark, New Jersey 25 April 1906; admitted to New Jersey Bar 1931; practised in Newark 1931-49; Superior Court Judge 1949-50; Appellate Division Judge 1950-52; Justice, Supreme Court of New Jersey 1952-56; Associate Justice, Supreme Court of the US 1956-90; married 1st 1928 Marjorie Leonard (died 1982; two sons, one daughter), 2nd 1983 Mary Fowler; died Arlington, Virginia 24 July 1997.