Kings. Although they come last, they really should come first, as Kings are where the Court Cards start. They are the fire - their element - the passion, the driving force. This is why Crowley has them as knights riding on horseback, rather than sitting passively on a throne. Kings are filled with energy, moving, leading, generating.
The thing to remember with the Kings, however, is that while they are powerful motivators, they are still "in the crown" - in the head. They can move mountains with their enthusiasm and energy and light a fire under almost anything. But they can't make it real all by themselves.
What they can do, like the Emperor is motivate, plan and command. The Queen is the one who will make it real, and the Knight/Prince will take it beyond the castle walls. But without the King, it won't happen at all. Thus, Kings in a spread can indicate motivation, a beginning or start of something.
As actual people, Kings stand for men (or women) who are leaders, planners or have high aspirations; they dream of having the best "kingdom" in the land. And they expect loyalty, especially from family and friends. They are men (or women) of influence and power; others come to them for advice and, being Kings, they're usually stubbornly sure that they're right.
Learn the Kings meaning in reversal in our reversed card meanings.