I found the following definition Merriam-Webster's Learner's Dictionary:
Deputy: an important assistant who helps the person who the leader of a government, organization, etc.
I think there's a grammar mistake here and it should be 'who is the leader ...'
Would anyone help me, please?
Thank you very much.
PS: Please let me know if there are any errors in my post.
Yes, either "who is the leader" or "who leads."
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.