According to Irish folklore, the first Irishman was a Spaniard named Milo who sailed in a barrel from Iberia to [H]iber[n]ia. Recent DNA genome testing has revealed the legend to be true. As Bryan Sykes writes in his book Blood of the Isles (2006), "the genetic evidence shows that a large proportion of Irish Celts, on both the male and female side, did arrive from Iberia at or the same time as farming reached the Isles." Moreover, linguists also now believe that the Gaelic language (Goidelic) is derived from Euskadi (the Basque language).
The largest Irish migration prior to the Great Potato Famine of 1848 was to Spain in the 17th and 18th centuries. The Irish, who were awarded Spanish citizenship on arriving in Spain as persecuted Catholics, joined the Spanish army's Hibernian regiments and became Spain's best soldiers and most famous generals. Many of these were posted in Cuba and married into the island's aristocracy, establishing our own great Irish-Cuban families (the O'Farrills, the O'Reillys, the Kindelans, the Madans, the Duanys, the O'Gabans, the Coppingers and the O'Naughtens).
Four Captains General of Cuba were of Irish origin (Nicolás Mahy; Sebastián Kindelán; Leopoldo O'Donnell and Luís Prendergast). On the other end of the social scale, some 378 Irish laborers contracted in New York built Cuba's first railroad in 1835. They also hold the distinction of staging the island's first strike. Most remained in Cuba because Spain refused to repatriate them.
In Cuba's Wars of Independence, the most famous of the many Irishmen who fought for our freedom was Canadian-born General William A.C. Ryan, who after a short but brilliant career as inspector and chief of calvary in Camagüey was captured aboard the American vessel Virginius and executed by the Spanish at age 30; and Captain "Dynamite Johnny" O'Brien, owner of the steamer Bermuda, one of the most daring and successful gunrunners to Cuba who also safely transported General Calixto García there.
Also of Irish extraction was the poet Bonifacio Byrne, whose "Ode to the Cuban Flag" is the most famous Cuban patriotic poem.
Eamon de Valera, Father of the Republic of Eire, was the Brooklyn-born son of a 19th century Cuban émigré and an Irishwoman.
The Irish returned the favor with Ernesto Guevara y Lynch (how appropriate!) but we shall forgive them that this day.
Happy St. Patrick's Day!