In retrospect, "Guardians of the Galaxy Vol. 3" feels like the true capstone to the Marvel Cinematic Universe up through "Infinity War," because it finally addresses the last loose plot threads left untied after Thanos (and Bruce Banner and Tony Stark) snapped their fingers while wearing the Infinity Gauntlet.

Thanos' brief mid-credits appearance at the end of the first "Avengers" film in 2012 obscures the fact that his first full, substantive role was in the first "Guardians of the Galaxy" film in 2014.

This also makes Thanos the first of writer-director James Gunn's series of "bad dads" i...