Their characters are given in the sentence that follows: "Collectively, I think, but am not certain, they are the worst men in the regiment so far as genial blackguardism goes"[1]—that is, they are trouble to authority, and always on the lookout for petty gain; but Kipling is at pains never to suggest that they are evil or immoral.
They are representative of the admiration he has for the British Army—which he never sought to idealise as in any way perfect—as in the poems collected in Barrack-Room Ballads (1892), and also show his interest in, and respect for the "uneducated" classes.
[emphasis added][2]This shows not only the spelling of his speech, but indicates the articulate fluency with which he speaks (he has "the gift of the gab") and also demonstrates, if read aloud, Kipling's feeling for the rhythms and "swing" of Irish English.
Mulvaney is also representative of the stereotypical Irishman in that he drinks, and has lost all his good conduct pay and badges; but he is less typical in that he is an exemplary soldier in what he (and Kipling) thinks is important: he may be regularly Confined to Barracks for his misdemeanours (mostly for being drunk and disorderly)—he thinks this is fair enough - but he supports army traditions (The Three Musketeers shows him defending the tradition of Thursday half day working, more successfully that the rest of the regiment) and resents some "cruel bad treatment" by the Colonel in The God from the Machine: "Me that have saved the repitation av a ten times better man than him".
Yet as the story continues, we see Mulvaney not only rejected by the beautiful and virtuous Annie Bragin, but forced to see himself as others see him, a shallow cad driven solely by vanity and lust.
In "Black Jack" the story begins in the present, with an aging Mulvaney needlessly humiliated and punished with extra duty by callow, weak-willed Sergeant Mullins.
After his punishment is over for the day, Mulvaney, still in a rage, leads his friends several miles off base, where he tells the story of how he once prevented the murder of the cruel and immoral Sgt.
He is no coward, however; in the story "His Private Honour" Ortheris actually challenges an officer who has accidentally struck him to a fist fight, and inflicts considerable damage even though he is ultimately knocked out.
Ortheris is the only member of the Soldiers Three who expresses a desire to rise in society, perhaps because he is the product of a modern big city, London, and has a skilled trade as a taxidermist.
One of the most tragic and powerful stories in the Soldiers Three collection, however, "On Greenhow Hill," details John Learoyd's past in memorable fashion and explains why he joined the army.