Final answer:
C. Wright Mills is the sociologist who argued that true power is rooted in control over institutions, which he described as 'power elite'. G. William Domhoff expanded on this concept, showing how power elites influence society's structure and maintain their status.
Step-by-step explanation:
The 20th-century sociologist you are referring to is C. Wright Mills, who introduced the concept of the 'power elite' in his 1956 book, 'The Power Elite'. Mills' work suggested that true power is consolidated in the hands of a small, privileged group that governs and controls society's major institutions. This small group, according to Mills, uses government and policies to maintain and strengthen their wealth and position.
Another sociologist, G. William Domhoff, further elaborated on the concept of power elites and their control over societal structures. Domhoff's insights reveal how these elites not only control institutions but also follow similar social patterns, reinforcing their dominance in society.