(Here, Lee is in the subjective case because it's the subject of is, and editor is in the subjective case because it's a subject complement; i.e., it renames the subject.)
It was I.
(Here, It is in the subjective case because it's the subject of was, and I is in the subjective case because it's a subject complement; i.e., it renames the subject.)
Only Pronouns Change Their Forms
In modern English, nouns do not change their forms in any of the cases (other than the possessive case). For example:
The man saw the dog.
(Here, man is in the subjective case because it's the subject of saw.)
The dog saw the man.
(This time, man is in the objective case, but there has been no change in spelling.)
Pronouns, however, do change their forms depending on their case. The subjective pronouns are I, you, he, she, it, we, they, who, and whoever. Look at this example:
I saw the dog. The dog saw me.
(I is the subject of the verb saw. It is a subjective pronoun. However, it changes to me when it is not in the subjective case; i.e., when it's not the subject of a verb or a subject complement.)
