Lord Donaldson, former Master of the Rolls, has died aged 84.
The judge was known for being open and approachable
He was the third most senior judge in England and Wales between 1982 and 1992, and was known for playing a key role in modernising the courts.
He presided at the Maguire Seven trial in 1976. Their convictions for IRA bomb-making were later quashed.
He was recently among a number of senior judicial figures who hit out at politicians calling on judges not to block anti-terrorism proposals.
The widower died unexpectedly at his home in Lymington, Hampshire, on Wednesday, his son Michael said.
Lord Donaldson leaves two daughters Margaret-Ann and Jennifer, as well as his son.
His wife, Dame Mary, had become the first woman Lord Mayor of London in 1983 and died in 2003.
During his judicial career he was considered to be an approachable man, and took the unusual step of listing his home phone number in Who's Who.
In court he was known for sucking boiled sweets and wearing his judicial wig at an angle.
The judge won praise for his reforms as head of the civil division of the court of Appeal - Master of the Rolls - where he tackled backlogs and time-wasting practices, and introduced computerisation.
Current Master of the Rolls, Lord Phillips, said in a statement: "John Donaldson was a judge of outstanding intellect, which he brought to bear to great effect in the civil justice system.
Lord Donaldson's wife died in 2003
"He dealt with civil work with unprecedented despatch, enabled by his ability to see the point at a very early stage of an appeal.
"He was undoubtedly a great Master of the Rolls and he will be missed."
After retiring from the judiciary, Lord Donaldson did battle with the government over the ban on hunting with dogs.
He made major contributions to the development of maritime law, among them chairing an inquiry set up after the 1993 Braer oil tanker ran aground off the Shetland Isles.
The Lord Chief Justice of England and Wales, Lord Woolf, said in a statement: "John Donaldson was a great judge who continued to make a valuable contribution to public life well into his retirement.
"He will probably be best remembered for his innovative ideas in many areas of the law.
"He made a particular contribution of great importance to the effective and efficient disposal of public law cases.
"He also made a significant contribution in the difficult field of employment law.
"Finally, he was a very distinguished commercial and admiralty judge.
"He was a man of great charm, and was extraordinarily quick-witted with a great sense of fun.
"He will be very much missed by his colleagues in the courts and the House of Lords."