Following your line of works, pleasant and of great interest, @honeydue. I believe that the companion par excellence of universal literature is Sancho Panza, who comes to occupy a place as important as Don Quixote in the history of the novel. There is a previous one that is confused with a guide, but that accompanies the main character during almost all his journey and his revelations: I am referring to the Virgil of the Divine Comedy that accompanies Dante in his passage through Hell and Purgatory. The companion, who would fall into the category of what some scholars call assistant or ally, usually plays a major role in the recognition ("anagnorisis") experienced by the protagonists.
One of the companions taken from films I remember most fondly is Alfredo, the projectionist of that beautiful and moving Italian film in homage to cinema, entitled *Cinema Paradiso".
Greetings.