Explanation
-(으)로서 marks the role or status someone acts in: -로서 after a vowel or ㄹ (친구로서, 수학자로서), -으로서 after any other consonant (학생으로서). Keep it apart from -(으)로써, which marks the means or tool (말로써); in speech both often collapse to plain -(으)로. 부모로서 할 수 있는 건 다 했어요. — As a parent I did everything I could.