In a candid profile of the ex- Fianna Fail leader, former US Ambassador Thomas Foley described Mr Cowen as "burly and brusque" and said he had "a reputation of not being much concerned with his public image."
The ambassador also described Mr Cowen's fondness for frequenting pubs and singing, saying he would likely be more approachable than his predecessor Bertie Ahern.
Ambassador Foley made the remarks -- in a cable marked "confidential" -- just days before Mr Cowen succeeded Mr Ahern as Taoiseach in May 2008.
The comments were circulated to the office of then US Secretary of State Condoleezza Rice and to every American embassy within the EU.
"Cowen is very popular among the rank and file Fianna Fail members, who affectionately refer to him (as he also refers to himself) as 'BIFFO', which commonly stands for 'Big, Ignorant F--cker from Offaly'," Mr Foley wrote.
The tone of the cable was largely positive, something that would change in later diplomatic dispatches as Mr Cowen lurched from crisis to crisis.
However, at the time of his elevation, US officials were very impressed with Mr Cowen's career, particularly his work on the Northern Ireland peace process while he was Minister for Foreign Affairs.
Ambassador Foley told Washington that having Mr Cowen as Taoiseach would be beneficial to US interests as he was "more affable and approachable" than Mr Ahern, who regarded as "a sociable loner".
Mr Foley described Mr Cowen as having a "raucous, combative style of arguing" and "a reputation as a formidable debater" who was "known for his direct approach to negotiations".
He said Mr Cowen liked "to socialise with his constituents in local pubs" and had "a good sense of humour", but did "not suffer fools gladly". He added Mr Cowen was "known as having a good singing voice."
Other leaked cables reveal US diplomats were talking about Mr Cowen as a potential Taoiseach as far back as 2004.
However, the embassy's opinion of his capabilities grew remarkably less favourable after he came to power.
Some cables suggest Mr Cowen failed to heed warning signs about the economy.
In June 2008, Mr Cowen told Ambassador Foley media reports on the faltering economy were "exaggerated" and he was "not too worried" about it.
Mr Cowen also wrongly predicted to the ambassador that the construction industry would "rebound" the following year.
The same month, after the government failed to get the first Lisbon Treaty referendum passed, the ambassador told Washington that Mr Cowen "genuinely appeared to be unsure of the way forward".
The embassy's opinion of Mr Cowen had fallen further by October 2008 when Ambassador Foley described Mr Cowen's failure to get the treaty ratified as "remarkable".
In the same cable, the ambassador also described how the furore over plans to eliminate automatic free medical cards for over-70s "reinforced a perception that Cowen's authority and credibility are slipping away and that he is out of touch with the people of Ireland".