The correct option is A Plaintiff
'A person who initiates a lawsuit in a court of law' is Option A 'Plaintiff'. Option B 'Litigant' is a person fighting legal case. Option C 'Deponent' is a person who testifies under oath, especially in writing. Option D 'Defendant' is person or company accused of having some something illegal. Thus, options B, C and D are incorrect and the correct option is Option A, Plaintiff.