This is the 12272nd most frequent Russian word.
исполнявший
"Исполнявший" means "one who performed" or "was fulfilling" in English, typically referring to a past action.
The word 'исполнявшим' here is in instrumental case, describing the musician performing melodies in a past continuous sense.
Он был музыкантом, исполнявшим мелодии на сцене.
He was a musician who performed melodies on stage.
The word 'исполнявшего' here is in accusative case, referring to the actor performing the leading role.
Режиссёр видел актёра, исполнявшего главную роль в спектакле.
The director saw the actor who performed the leading role in the play.
The word 'исполнявший' here is nominative singular, describing the day fulfilling their dreams in a personified way.