Question: Who was the first Irish playwright of note to write about the Dublin working classes, Colson Whitehead or Seán O'Casey ?

Context paragraphs:
Red Roses for Me (play): Red Roses for Me is a four-act play written by Irish playwright Seán O'Casey which premiered at the Olympia Theatre in Dublin in 1943.  The story is set against the backdrop of the Dublin Lockout of 1913, events in which O'Casey himself had participated.

Sybil (novel): Sybil, or The Two Nations is an 1845 novel by Benjamin Disraeli.  Published in the same year as Friedrich Engels's "The Condition of the Working Class in England in 1844", "Sybil" traces the plight of the working classes of England.  Disraeli was interested in dealing with the horrific conditions in which the majority of England's working classes lived — or, what is generally called the Condition of England question.

Zone One: Zone One is a 2011 "The New York Times" best-selling novel by African American author Colson Whitehead.  "Zone One" is part genre fiction, part literary fiction—a zombie story in the hands of a Pulitzer-nominated novelist.  Whitehead has stated that the novel was partly an attempt to return to his adolescent fascination with horror writer Stephen King and science fiction icon Isaac Asimov.

Labor history (discipline): Labor history or labour history is a sub-discipline of Social History which specialises on the history of the working classes and the labor movement.  The central concerns of labor historians include industrial relations and forms of labor protest (strikes, lock-outs), the rise of mass politics (especially the rise of Socialism) and the social and cultural history of the industrial working classes.  Labor historians may also concern themselves with issues of gender, race, ethnicity and other factors besides class but chiefly focus on urban or industrial societies which distinguishes it from Rural history.

Sag Harbor (novel): Sag Harbor is a 2009 novel by award-winning author Colson Whitehead.

Colson Whitehead: Colson Whitehead (born November 6, 1969) is an American novelist.  He is the author of six novels, including his debut work, the 1999 novel "The Intuitionist", and "The Underground Railroad" (2016), for which he won the 2016 National Book Award for Fiction and the 2017 Pulitzer Prize for Fiction.  He has also published two books of non-fiction.  In 2002, he received a MacArthur Fellowship ("Genius Grant").

U and non-U English: U and non-U English usage, with "U" standing for "upper class", and "non-U" representing the aspiring middle classes, was part of the terminology of popular discourse of social dialects (sociolects) in Britain in the 1950s.  The debate did not concern itself with the speech of the working classes, who in many instances used the same words as the upper classes.  For this reason, the different vocabularies often can appear quite counter-intuitive: the middle classes prefer "fancy" or fashionable words, even neologisms and often euphemisms, in attempts to make themselves sound more refined ("posher than posh"), while the upper classes in many cases stick to the same plain and traditional words that the working classes also use, as, confident in the security of their social position, they have no need to seek to display refinement.

Seán O'Casey: Seán O'Casey ( ; Irish: "Seán Ó Cathasaigh" , ] ; born John Casey, 30 March 1880 – 18 September 1964) was an Irish dramatist and memoirist.  A committed socialist, he was the first Irish playwright of note to write about the Dublin working classes.

The Silver Tassie (play): The Silver Tassie is a four-act Expressionist play about the First World War, written between 1927 and 1928 by the Irish playwright Seán O'Casey.  It was O'Casey's fourth play and attacks imperialist wars and the suffering that they cause.  O'Casey described the play as "A generous handful of stones, aimed indiscriminately, with the aim of breaking a few windows.  I don't think it makes a good play, but it's a remarkable one."

Marxism and religion: The nineteenth-century German thinker Karl Marx, the founder and primary theorist of Marxism, had an antithetical and complex attitude to religion, viewing it primarily as "the soul of soulless conditions", the "opium of the people" that had been useful to the ruling classes since it gave the working classes false hope for millennia.  At the same time Marx saw religion as a form of protest by the working classes against their poor economic conditions and their alienation.

Supporting paragraphs: Seán O'Casey Colson Whitehead
Answer: Seán O'Casey