grateful to him ... for

[navi tasan]

1-I am grateful to him more than to any other writer for a series of wonderful short stories.
2-I am grateful to him more than to any other writer, for a series of wonderful short stories.

Are the sentences correct and is the comma necessary.

I think it is. I think '1' means

3-I am grateful to him for a series of wonderful short stories more than I am grateful to any other writer for a series of wonderful short stories.

That can't possibly be the intended meaning.

Gratefully,
Navi.

 

[probus]

A comma is not usually a precision tool. I agree that 3 is a highly unlikely interpretation, but I think that very few readers would be tempted to think of it. The great majority of readers would correctly interpret 1. In fact, the comma in 2 strikes me as odd, although I understand your reason for including it, and if you think about it it does remove the potential ambiguity.