Michael O'Riordan (Irish: Mícheál Ó Ríordáin; 12 November 1917 – 18 May 2006) was the founder of the Communist Party of Ireland (3rd) and also fought with the Connolly Column in the International Brigades during the Spanish Civil War.

They were motivated in part by enmity towards the 800 or so Blueshirts, led by Eoin O'Duffy who went to Spain to fight on the "nationalist" side in the Irish Brigade.

As a result of his IRA activities, during the Second World War, or the Emergency as it was known in neutral Ireland, he was interned in the Curragh internment camp from 1939 until 1943 where he was Officer Commanding of the Cork Hut and partook in Máirtín Ó Cadhain's Gaelic League classes as well as publishing Splannc (Irish for "Spark", named after Lenin's newspaper).

[5] The branch was initially established by former members of the Curragh Camp's Communist Group, including Bill Nagle and Jim Savage.

[5][7] In 2001, O'Riordan would claim that any attempt to raise the issue of defence of communist Spain "was shouted down at Labour Party Conferences".

[8] In 1945 he was a founding secretary of the Cork Socialist Party,[9] whose other notable members included Derry Kelleher, Kevin Neville, Máire Keohane-Sheehan [note 1] and Thomas Murray.

[10][11][12] O'Riordan subsequently worked as a bus conductor in Cork and was active in the Irish Transport and General Workers Union (ITGWU).

[9] Afterwards, he moved to Dublin where he lived in Victoria St with his wife Kay, continued to work as a bus conductor and remained active in the Irish Transport and General Workers Union.

In 1966 he attended the International Brigades' Reunion in Berlin and was instrumental in having Frank Ryan's remains repatriated from Germany to Ireland in 1979.

O'Riordan staunchly pro-Soviet direction of the party led to a number of members leaving to form the Eurocommunist Irish Marxist Society.

[20] His last major public outing was in 2005 at the re-dedication of the memorial outside Dublin's Liberty Hall to the Irish veterans of the Spanish Civil War.

The book was the inspiration for Irish singer-songwriter Christy Moore's famous song Viva la Quinta Brigada.

Then Labour Party leader Ruairi Quinn praised O'Riordan after his death, saying; "As leader of the Labour Party I had the honour of ensuring he received a special citation at our 2001 national conference Michael O'Riordan stood out against the tide of Irish conservatism and clerical domination that kept Ireland backward and isolated in the 1930s, 1940s and 1950s.

Following a wake the previous night at Finglas Rd, hundreds turned up outside the house of his son Manus and traffic ground to a halt as family, friends and comrades – many of whom were waving the red flag of the Communist Party of Ireland – escorted O'Riordan to Glasnevin Cemetery.

Actors Patrick Bergin, Jer O'Leary; singer Ronnie Drew; artist Robert Ballagh; newsreader Anne Doyle were also among the mourners.

Tributes and were paid by President of Ireland Mary McAleese, Taoiseach Bertie Ahern, Sinn Féin leader Gerry Adams and Labour Party TDs Ruairi Quinn and Michael D. Higgins.