Kirk in "The Man Trap" on the night of September 8, 1966 was a cold, calculating hardass. In "I, Mudd" just a little over a year later he's full of wit and humor and goofy scheming to foil the crew's human and android adversaries, then in TMP is back to being more of an unsmiling hardass before swinging more human and being a more warm and embracing individual in the following TOS Era movies. Shatner was all over the place for nearly 30 years, in part because the role required him to evolve and change with the stories and be all over the place.