Former public servant and economist TK Whitaker has died aged 100 in Dublin.
Described by several taoisigh as the State's finest public servant, he was named Irish Man of the 20th century in a public vote in 2001.
His pioneering work in the Department of Finance set the blueprint for a radical plan that reversed the country's economic woes in the early 1960's.
Dr Whitaker had celebrated his 100th birthday last month.
Tonight, in a statement Taoiseach Enda Kenny described TK Whitaker as "in every sense a national treasure".
Mr Kenny added: "He had an innate understanding of our patrimony - what we inherit from our ancestors - our ingenuity, our elegance, our intellect, our artistry, industry and kindness, and how we could put this to work for our country and our people.
"TK Whitaker changed life, lives and generations in Ireland. In the last decades, he more than any other person was responsible for transforming our economy and public life.
"He had a rare vision for our country and its future. He was a gentleman and patriot. Today, as a nation, we mourn the passing of this outstanding man. We celebrate and give thanks for his exemplary achievements on behalf of Ireland.
"In modern Irish history, TK Whitaker is both incomparable and irreplaceable.
"Truly, ní bheidh a leithéid ann arís."
Thomas Kenneth Whitaker was just 39 years old when he was appointed to the top job at the Department of Finance in 1955.
The civil servant born in Co Down and raised in Drogheda took over as Secretary General at the Department when the economy was in a dire state.
He concluded that a radical new approach was required. This thinking resulted in the First Programme for Economic Expansion and was embraced by Taoiseach Sean Lemass.
It would increase foreign investment in Ireland, spur economic growth and cut unemployment rates.
In 1965, Whitaker would also help organise an unprecedented meeting between Taoiseach Sean Lemass and the Prime Minster of Northern Ireland Terence O'Neill.
While this early effort at reconciliation was unsuccessful - it did undoubtedly lay the foundations for future agreements in the North.
In 1969 he became Governor of the Central Bank and after retiring from that role he was twice appointed to Seanad Éireann.
For 20 years up to 1996 he was chancellor of the National University of Ireland.
But perhaps his most enduring legacy was his determination to change the economic thinking of politicians here in the late 1950s.