James T. Kirk/Appendices/Background information/Character development

Gene Roddenberry, in his original pitch to television producers, described the character (originally named Robert April, then Christopher Pike) that later came to be known, eventually, as Captain Kirk:
The 'skipper, about thirty-four, Academy graduate, rank of Captain... a shorthand sketch of Robert April might be 'A space-age Captain Horatio Hornblower', lean and capable both mentally and physically.
A colorfully complex personality, he is capable of action and decision that can verge on the heroic – and at the same time lives a continual battle with self-doubt and the loneliness of command.
As with similar men in the past (Drake, Cook, Bougainville, and Scott), his primary weakness is a predilection to action over administration, a temptation to take the greatest risks onto himself. But, unlike most early explorers, he has an almost compulsive compassion for the plight of others, alien as well as human, [and] must continually fight the temptation to risk many to save one.
NBC's early- sales brochure (reprinted in Inside Star Trek: The Real Story) described Kirk thus:
A Space Academy graduate, Captain James Kirk has learned to accept the loneliness of command as he has rapidly climbed the ladder of promotion, although he never will learn to like the loneliness his post brings. Starship command is the most important position a man in the Space Service can hold, since he alone can and must make decisions in his contact with the other worlds that can affect the future course of civilization throughout the Universe. So far, James Kirk has proven himself equal to this awesome responsibility. A strong, capable, highly intelligent man in his mid-thirties, Kirk is a born leader, who has trained himself to walk the tightrope between friendship and authority without losing his sense of humor or compassion for others.
William Shatner was to have reprised his role as Captain Kirk on Star Trek: Phase II. The writers/directors guide for that series, written, among others, by Gene Roddenberry and Jon Povill between May and , described Kirk as follows:
A shorthand sketch of Kirk might be 'a space-age Captain Horatio Hornblower,' constantly on trial with himself, a strong, complex personality.
With the Starship out of communication with Earth and Starfleet bases for long periods of time, a Starship captain has unusual broad powers over both the lives and welfare of his crew, as well as over Earth people and activities encountered during these voyages. He also has broad power as an Earth Ambassador may discover. Kirk feels these responsibilities strongly and is fully capable of letting the worry and frustration lead him into error.
He is also capable of fatigue and inclined to push himself beyond Human limits, then condemn himself because he is not superhuman. The crew respects him, some almost to the point of adoration. At the same time, no senior officer aboard is fearful of using his own intelligence in questioning Kirk's orders and can themselves be strongly articulate up to the point where Kirk signifies his decision has been made.
Kirk is a veteran of hundreds of planet landings and space emergencies. He has a broad and highly mature perspective on command, fellow crewmen, and even on alien life customs, however strange or repugnant they seem when reassessed against Earth standards.
On the other hand, don't play Kirk like the captain of an 1812 frigate in which nothing or no one moves without his command. The Enterprise crew is a finely-trained team, well able to anticipate information and action Kirk needs.
Aboard ship, Captain Kirk has only a few opportunities for anything approaching friendship. One exception is with ship's surgeon Dr. McCoy, who has a legitimate professional need to constantly be aware of the state of the Captain's mind and emotions. But on a 'shore leave' away from the confines of self-imposed discipline, Jim Kirk is likely to play pretty hard, almost compulsively so. It is not impossible he will let this drag him at one time or another into an unwise romantic liaison which he will have great difficulty disentangling. He is, in short, a strong man forced by the requirements of his ship and career into the often lonely role of command, even lonelier because Starship command is the most difficult and demanding task of his century.