[Man in the macintosh spoilers]

"Now who is that lankylooking galoot over there in the macintosh? Now who is he I'd like to know? Now, I'd give a trifle to know who he is. Always someone turns up you never dreamt of." p105

"Mr Bloom stood far back, his hat in his hand, counting the bared heads. Twelve. I’m thirteen. No. The chap in the macintosh is thirteen. Death’s number. Where the deuce did he pop out of? He wasn’t in the chapel, that I’ll swear. Silly superstition that about thirteen."

" -- And tell us, Hynes said, do you know that fellow in the, fellow was over there in the...
He looked around.
-- Macintosh. Yes, I saw him, Mr Bloom said. Where is he now?
-- M'Intosh, Hynes said, scribbling. I don't know who he is. Is that his name?
He moved away, looking about him.
-- No, Mr Bloom began, turning and stopping. I say, Hynes!
Didn't hear. What? Where has he disappeared to? Not a sign. Well of all the. Has anybody here seen? Kay ee double ell. Become invisible. Good Lord, what became of him?"

"In Lower Mount street a pedestrian in a brown macintosh, eating dry bread, passed swiftly and unscathed across the viceroy's path." WRocks

"The man in the brown macintosh loves a lady who is dead." Cyclops

"The mourners included: Patk. Dignam (son), Bernard Corrigan (brother-in-law), Jno. Henry Menton, solr., Martin Cunningham, John Power .)eatondph 1/8 ador dorador douradora (must be where he called Monks the dayfather about Keyes's ad) Thomas Kernan, Simon Dedalus, Stephen Dedalus, B.A., Edw. J. Lambert, Cornelius Kelleher, Joseph M'C. Hynes, L. Boom, C.P. M'Coy,-- M'Intosh, and several others.
Nettled not a little by L. Boom (as it incorrectly stated) and the line of bitched type, but tickled to death simultaneously by C.P. M'Coy and Stephen Dedalus, B.A., who were conspicuous, needless to say, by their total absence (to say nothing of M'Intosh)" Eumeus

"Golly, whatten tunket's yon guy in the mackintosh? Dusty Rhodes. Peep at his wearables. By mighty! What's he got? Jubilee mutton. Bovril, by James. Wants it real bad. D'ye ken bare socks? Seedy cuss in the Richmond? Rawthere! Thought he had a deposit of lead in his penis. Trumpery insanity. Bartle the Bread we calls him. That, sir, was once a prosperous cit. Man all tattered and torn that married a maiden all forlorn. Slung her hook, she did. Here see lost love. Walking Mackintosh of lonely canyon. Tuck and turn in. Schedule time. Nix for the hornies. Pardon? See him today at a runefal? ...Pflaap! Pflaap! Blaze on. There she goes. Brigade!" Oxen

"London's burning, London's burning! On fire, on fire!...
(A man in a brown macintosh springs up through a trapdoor. He points an elongated finger at Bloom.)
THE MAN IN THE MACINTOSH
Don't you believe a word he says. That man is Leopold M'Intosh, the notorious fireraiser. His real name is Higgins." Circe

"What selfinvolved enigma did Bloom risen, going, gathering multicoloured multiform multitudinous garments, voluntarily apprehending, not comprehend?
Who was M'Intosh?" Ithaca

theories:

Capt Sinico or Mr Duffy from Painful Case

James Clarence Mangan

Joyce himself (Nabokov) "in the library episode known as "Scylla and Charybdis," where Stephen Dedalus explains how the great Shakespeare "has hidden his own name, a fair name, William, in the plays, a super here, a elown there, as a painter of old Italy set his face in a dark corner of his canvas..." (Ulysses, 221). This, as Nabokov concludes from evidence hinted at earlier on in his lecture, "is exactly what Joyce has done--setting his face in a dark corner of his canvas. The Man in the Brown Macintosh who passes through the dream of the book is no other than the author himself. Bloom glimpses his maker!"."

Rudolph Bloom's ghost (John Gordon, paywall) more

Joseph from Old Testament (Cosgrove, paywall)

arsonist (Barger)