Step 1: Understanding the Concept:
The question asks to identify the jurist most famously associated with the modern definition and systematic exposition of the 'Rule of Law'.
Step 3: Detailed Explanation:
The modern concept of the Rule of Law was most famously articulated by A.V. Dicey (misspelled as A.Y. Diecy in the question) in his book "Introduction to the Study of the Law of the Constitution" (1885). Dicey's theory of the Rule of Law has three main pillars:
1. Supremacy of Law: No person can be punished except for a distinct breach of law established in the ordinary legal manner before the ordinary courts. This implies the absence of arbitrary power.
2. Equality before the Law: Every person, whatever their rank or condition, is subject to the ordinary law of the land and the jurisdiction of ordinary courts.
3. Predominance of Legal Spirit: The general principles of the constitution are the result of judicial decisions determining the rights of private persons.
While the concept of law being supreme has ancient roots (e.g., Aristotle), the modern, systematic formulation that forms the basis of contemporary discussions is credited to Dicey.
Step 4: Final Answer:
The Rule of Law is most famously defined and explained by A.V. Dicey.