The following historical account highlights the evolution of controlled thermonuclear research (CTR) at Los Alamos (the singular entity denoted Los Alamos Laboratory/Los Alamos Scientific Laboratory/Los Alamos National Laboratory at different times in its evolution is designated “Los Alamos”) following the Manhattan Project. It focuses on magnetic fusion energy research performed by the Physics Division, Theory Division, and CTR Division from 1946 through 1990. It chronicles a compelling story, including the first laboratory demonstration worldwide of thermonuclear D-D fusion in 1960 by James Leslie Tuck and colleagues with the Scylla 1 theta pinch. Neither the rich history of Los Alamos research into inertial confinement fusion nor a summary of the historical breadth of fusion energy research worldwide is included. These subjects have been well researched and well documented in numerous publications, some of which are referenced herein.