Derek Nally was born in December 1936 in Thurles, Co Tipperary. The second-eldest of four children, he was educated at Thurles CBS and joined the Garda in 1957.
Seven years later he was promoted to sergeant. In 1971 he was appointed to the Garda Press Office, where he worked for two years before becoming general secretary of the Association of Garda Sergeants and Inspectors (AGSI).
He remained for 10 years in that position during one of the most turbulent times in the force's history. When he left the job, he was made a detective sergeant and was based in Enniscorthy, Co Wexford. However, he regards Bunclody, Co Wexford, as his home, having lived there since the 1960s.
Mr Nally has a history of working for the young and underprivileged. He chaired the National Federation of Youth Clubs from 1973 to 1975. In 1983, on leaving his AGSI post, he helped to found Victim Support in the Republic and was its first chairman. He is now its honorary president.
Over the last 15 years Mr Nally has built up a relatively large private investigation business. Now employing 30 people and based in Bunclody and in Dublin, and with offices in Northern Ireland, International Investigations covers a wide range of work. It is often hired by insurance companies and people searching for missing relatives.
Mr Nally married Ms Joan Bonass, from Dublin, and they have two adult daughters, Laurena and Louise.
Long before he thought of becoming a presidential candidate, Mr Nally had a high profile as head of AGSI and came to personify the organisation. He had made his mark as a sergeant in Co Wexford in the early 1960s, when gardai were in almost open revolt over what they regarded as a discriminatory pay award.
He was one of only five gardai in a division of 250 who dared to walk into a meeting on pay knowing the superintendent at the door was recording their names.
As AGSI general secretary, Mr Nally called for extra pay and powers for gardai and entered political debate when he sought effective extradition from Britain and Northern Ireland.
He also developed progressive ideas which might now be labelled a "liberal agenda". Mr Nally has for a long time argued that "crime has its roots in society" and has to be tackled with initiatives such as investment in deprived areas and diversion programmes for young offenders.
At a time of political interference in the Garda, he highlighted abuses of power and suggested they be made an offence.
He also "blew the whistle" on the tapping of journalists' telephones and on the so-called "heavy gang" of gardai who were using unorthodox methods when investigating crime.
Given the dubious, and in some cases impossible, confessions these gardai extracted, Mr Nally is unlikely to fear suggestions that unhappy members or former members of the force are planning an Adi Roche-style ambush on his candidacy.
According to Mr Pat Cox, the Independent MEP now working on his campaign, Mr Nally showed exceptional courage at the time. RTE's investigative current affairs television programmes could not survive on faceless criticisms of senior Garda management. However, at crucial times, Mr Nally agreed to go on air and make his allegations.
He says he told the then minister for justice, Mr Paddy Cooney, about the "heavy gang" and also had a meeting with Dr Garret FitzGerald, when he was leader of the opposition, to express his concerns about events.
Mr Nally has always maintained these moves were for the good of the force. "There's nobody prouder of the Garda Siochana than I am," he says.
As a private investigator, Mr Nally was in the spotlight again in the early 1990s when he starred in a Channel Four "fly-on-the-wall" documentary called Looking for Billy, part of the Cutting Edge series. It followed Mr Nally and his investigators as they tried to track a missing Irishman in Britain.
Part of Mr Nally's success as an investigator is the network of older and retired gardai who can help him. There is hardly a village in which he cannot name a contact to find out something he wishes to know.
The group of supporters who came to Dublin from Bunclody for the start of his campaign almost unanimously presented Mr Nally as a mixture of Santa Claus, trouble-shooter and moral compass. "If you have a problem, of if you need advice, you go to him and he'll sort it out," was their refrain.