Friedman’s *Legal Theory* is a key resource for understanding the evolution of jurisprudential schools, including analytical, historical, and sociological approaches.
The expression 'Legal Theory' was coined by Wolfgang Friedman, a prominent jurist known for his work in jurisprudence. His book, *Legal Theory* (1944), is a seminal text that explores various schools of jurisprudential thought. Thus, the correct answer is:
\[
{\text{Friedman}}
\]