A childhood friend of murdered spy Gareth Williams described him as academically gifted by socially naive today.
Dylan Parry, 34, said the GCHQ codes and cyphers expert was an isolated child fascinated by mathematics and computers.
Mr Parry, a volunteer at Westminster Cathedral, went to school with Mr Williams at Uwchradd Bodedern secondary in Anglesey, North Wales.
He told the London Evening Standard that Mr Williams travelled to Bangor University every week aged 16 to study for a mathematics degree part-time.
He said: "He was the kind of person who found it difficult to engage with people on a normal level.
"It was clear he was going to go far, but we all assumed he would end up in academia. Finding out he became a spy was a shock."
Mr Parry added that his friend was someone "people could easily take advantage of", that he was "naive" and a poor judge of character.
A detailed picture of an athletic, intelligent and extremely private man was emerging today as police continue to hunt for Mr Williams' killer.
The spy died while on secondment to the Secret Intelligence Service (MI6) from his work at Government Communications HQ (GCHQ) in Cheltenham.
Mr Williams attended Uwchradd Bodedern high school on Anglesey, before graduating with a first class mathematics degree from Bangor University aged 19.
He continued his studies with an elite course at St Catharine's College, Cambridge, but dropped out after apparently failing an exam.
The university is one of the traditional hunting grounds for recruiters looking for bright young things to join the intelligence community.
Mr William's father, Ian, works at Wylfa nuclear power station and only returned from holiday in Canada and America with his wife Ellen yesterday.
The couple, who live in Valley, Anglesey, went straight to London with their daughter, Ceri, who lives near Wrexham.
His mother's cousin William Hughes, an Anglesey councillor, said the victim worked for GCHQ, the government's so-called listening post, for "many years".
But he keep quiet regarding the actual nature of his work. "He would never talk about it and it felt rude to ask," Mr Hughes said.
Jenny Elliott, his former landlady in Cheltenham, described Mr Williams as "a lovely guy".
She added that he was often sent overseas, spending much of this time in America, even though he disliked flying.
Residents close to his London address said Mr Williams was "extremely friendly" and was often seen on his racing bicycle.
They said his curtains were always drawn and it was difficult to tell if anyone was in his smart two-storey Pimlico flat.
Fellow members of the Cheltenham & Country Cycle Club said he turned up to race at events, often very successfully, but did not join in socially.
They described him as a quiet man who did not go to the pub, but was extremely polite and amiable.