Okay I apologize in advance for adding commentary but this is post IS VERY IMPORTANT.
Olaf is NOT just a silly device for the sake of comic relief. He could be described as the equivalent of a character or imaginary friend created by Anna and Elsa. Yes he is childish, but he is literally the result of the imaginations of two toddlers. All he really knows is what they subconsciously bestowed upon him at the time, when they couldn’t have been any older than 6 and 3. He is them, and he’s their connection. Olaf is important.
I love when you guys add commentary! Because that’s exactly what I wanted this photoset to show. I get annoyed when people call Olaf ‘completely useless.’ Now certainly you can find him annoying or not like him, but he wasn’t useless. Right when he shows up his purpose is to show Anna the way to Elsa’s castle and also, just as importantly, he is a shout-out to Anna that hey your sister does miss you (at this point she can’t be 100% sure since Elsa ran away). He is a constant reminder of the closeness they had as kids. So yeah Olaf is the comedic relief (it’s a kids movie after all) but I think they did a great job at making his character have more meaning than most comedic relief characters.
Also that Olaf holds the happy memories and the playful Elsa, where as Marshmallow is the side of Elsa that had to push people away.