Former students recall "riveting" lectures from a man inclined to say: "There are three sides to this problem." His own research is dispersed on a need to know basis, a secretive quality that has made him the guardian of a goldmine of intelligence information.
"He enjoys keeping his own projects under cover. It is a bit of a joke between us. We try and find out what he is doing but he is always discreet," said a fellow academic.
For several years, Professor Andrew, 58, diligently analysed the archives handed over by Vasili Mitrokhin, a Russian defector, without a leak.
Yet he is no stranger to the public eye. His has long been the most authoritative voice on British intelligence, he is a frequent media commentator, an accomplished television presenter and a prolific author.
President Bill Clinton is said to have handed an inscribed copy of Professor Andrew's book on the United States secret service, For the President's Eyes Only, to his head of intelligence, John Deutch.
The involvement of Professor Andrew, a Cambridge don of modern and contemporary history, in the secret dossier that has formed the basis of The Mitrokhin Archive, has caused little surprise to those in the field. Having co-authored four volumes with the high-profile KGB defector Oleg Gordievsky, it was well-charted territory for him.
A fellow intelligence expert said: "He is quite stunning and has formidable timing. He wrote the best book on British intelligence, the best on the KGB and the best on American intelligence. Punctually every five years he brings out another brilliant book.
"His relaxed and disarming persona belies the hard work underneath."
Professor Andrew is a trusted figure in the intelligence establishment, many of whom view him as their unofficial historian. Instead of risking the Mitrokhin archives falling into the hands of a maverick, MI5 could feel quite secure that the professor provided a pair of "safe hands".
Despite brief visiting professorships abroad, Professor Andrew has rarely strayed far from Cambridge. He arrived at Corpus Christi College as an undergraduate in the early Sixties, when he married Jennifer Garratt. The couple have a son and two daughters.
After a history double first and a PhD on French foreign policy before the First World War, he gained a research fellowships at Gonville and Caius College alongside Stephen Hawking.
In 1985, he wrote Secret Service: The Making of the British Intelligence Community and in 1990 he co-wrote the first of the Gordievsky books about the KGB. Shortly afterwards he met Colonel Vasili Mitrokhin with his secret files of KGB operations from 1917.
Motivated by ideals rather than finances, defection had been on Mitrokhin's mind long before he retired in 1984. He had systematically copied thousands of files, buried them in waterproof trunks in a secret location and bided his time.
Just after the end of the Cold War, Mitrokhin approached the CIA and offered to defect but was turned down.MI6 took a different view when he approached their officers in Latvia. In December 1992 they smuggled Mitrokhin, his family, and six large trunks of files out of Russia into Britain.
MI6 handed Mitrokhin and his archive to MI5, who would have carefully debriefed the former KGB man. An analysis of the material found it capable of demonstrating the strengths and weaknesses of Western intelligence and counter intelligence over 60 years.
In the mid 1990s British intelligence decided that their "coup" should be made public and introduced Mitrokhin to Professor Christopher Andrew.
MI5's lack of action over the Mitrokhin archive - not passing a summary to the Conservative Home Secretary - suggests that they did not grasp the impact the material would have.
Professor Andrew did. Yesterday some insiders said that the choice of Andrew was symptomatic of the disregard for freedom of information that still abounds within the secret services. They complained that the archives should have been placed in the public record office for all to see.
Instead they were channelled through one man, a trusted insider who sits on a goldmine of intelligence history.