All his life, we are glad to note, our Person had experienced the curious sensation (known to three famous theologians and two minor poets) of there existing behind him - at his shoulder, as it were - a larger, incredibly wiser, calmer and stronger stranger, morally better than he. This was, in fact, his main "umbral companion" (a clownish critic had taken R. to task for that epithet) and had he been without that transparent shadow, we would not have bothered to speak about our dear Person. During the short stretch between his chair in the lounge and the girl's adorable neck, plump lips, long eyelashes, veiled charms, Person was conscious of something or somebody warning him that he should leave Witt there and then for Verona, Florence, Rome, Taormina, if Stresa was out. He did not heed his shadow, and fundamentally he may have been right. We thought that he had in him a few years of animal pleasure; we were ready to waft that girl into his bed, but after all it was for him to decide, for him to die, if he wished. (TT, chapter 25)

Roman letter R is the mirror image of Cyrillic Я (pronounced ya and being Russian first person pronoun that corresponds to English "I").* In Turgenev's story After Death (Klara Milich, 1883), the hero feels that somebody stands in the middle of his room, near to him, and breathes lightly. Then a gentle noiseless whirlwind rushes through the room, over him, through him, and Aratov clearly hears the word "Я!" ("I"):

Аратов решился заснуть на этот раз... Но в нём возникло новое ощущение. Ему показалось, что кто-то стоит посреди комнаты, недалеко от него -- и чуть заметно дышит. Он поспешно обернулся, раскрыл глаза... Но что же можно было видеть в этой непроницаемой темноте? Он стал отыскивать спичку на ночном столике... и вдруг ему почудилось, что какой-то мягкий, бесшумный вихрь пронёсся через всю комнату, через него, сквозь него -- и слово "Я!" явственно раздалось в его ушах.

It seems to me that the ghostly narrator in TT, Mr. R. (who has a long German name, in two installments, with a nobiliary particle between castle and crag) has nothing to do with Adam von Librikov** (a character in one of R.'s books) or "another American writer, also residing in Switzerland," who is visited by Hugh Person (TT, chapter 18). His acronym merely hints at the Russian one-letter word heard by Aratov. Btw., Schiller's dukhi (Geister; spirits) are mentioned in Klara Milich. One is also reminded of Shekspirovy dukhi (Shakespeare's Ghosts, 1825), Kuechelbecker's "Dramatic Joke in two acts."

Its name [of the Stresa hotel where the Persons stayed during their honeymoon], he [HP] said, sounded like "Beau Romeo." (TT, 25) Romeo is an anagram of Moore (a friend of Hugh's wife Armande, Julia Moore is R.' stepdaughter whom R. debauched and whom Hugh Person also once possessed).

In his deathbed delirium Aratov calls himself Romeo after poisoning: В предсмертном бреду Аратов называл себя Ромео после отравы, говорил о заключённом, о совершённом браке; о том, что он знает теперь, что такое наслаждение. (Klara Milich, chapter 18)

Btw., Oscar Wilde stole Klara Milich (the gifted actress who takes poison before appearing in her last stage performance) from Turgenev renaming her Sybil Vane in The Picture of Dorian Gray. Nevertheless, in VN's story The Vane Sisters the spirit of Oscar Wilde accuses Cynthia's and Sybil's dead parents of plagiatisme.