Edwin Arlington Robinson is the author of Richard Cory and using specific words(diction) to convey a magestic sense to Cory but in a sarcastic or ironical manner.
For example "...from sole to crown" "...he glittered when he walked" "...richer than a king"
"Clean favored and imperially slim" , "And he was always quietly arrayed" these are some exaples to show his majesty. In addition, "and admirably schooled in every grace..."
He uses these words to show how Cory is seen by other people. His tone is admiration.However later in the poem, we can detect irony.