Jecht is a creation of Square Soft and is a motivation/background character in Final Fantasy X. As the second, and elder Guardian for the Summoner Braska, Jecht and his interactions with Auron have a profound affect on the young warrior. Jecht does not appear in Legendary Guardian. He is the secondary protagonist in the stories Braska’s Journey and Bonds of Love.

Square does not give an official character description for Jecht on their web site. However, after much investigation and research I have determined the following:

Male – Age 35 at time of Braska's defeat of Sin. Jecht is the most famous Blitzball player in the history of the city of Zanarkand. Through unknown means, he is brought from his city of advanced technology to the realm of Spira - where Zanarkand is thought of as a holy place and has been in ruins for 1000 years. For unknown reasons, Jecht is thrown into a cell in the Bevelle temple near the entrance to the Via Purifico. Braska hears of his plight and bails him out, requesting that Jecht accompany he and Auron on their pilgrimage. The blitz star takes them up on the offer and the rest is pure game spoilers.
Jecht has a problem with alcohol and leaves behind him a wife (who remains nameless) and a boy named Tidus. Memories and spheres clearly show that Jecht deeply loves his son. In spite of this, he has a hard time showing it, and the relationship with the boy is very strained at best. He seems to have no concept of magic, no knowledge of the Church of Yevon, and to be completely at a loss about most of the world of Spira. He and Auron are shown doing a lot of verbal sparing and posturing, causing difficulty for their Summoner.

Without giving too much away, Jecht determines that he will never get back to his Zanarkand and forms a deep bond with Braska. He also, over the course of the pilgrimage, makes his peace with Auron and the two become very close. He was a cocky, mouthy, direct kind of guy. The artwork from Square shows him with a very large dual edged sword. However, since he also was a blitz player I believe he may have (like Wakka) used ball weapons in a pinch or when circumstances called for it.

In attempting to create Jecht for BJ and Bonds, I used the Kiersy Temperament Sorter. Jecht is an ESTP according to my interpretation. If you aren’t interested in checking out the full profile explanation, here’s a smattering of info:
ESTP - The Doer
ESTPs are outgoing, straight-shooting types. Enthusiastic and excitable, ESTPs are "doers" who live in the world of action. Blunt, straight-forward risk-takers, they are willing to plunge right into things and get their hands dirty. They live in the here-and-now, and place little importance on introspection or theory. The look at the facts of a situation, quickly decide what should be done, execute the action, and move on to the next thing.
ESTPs have an uncanny ability to perceive people's attitudes and motivations. They pick up on little cues which go completely unnoticed by most other types, such as facial expressions and stance. They're typically a couple of steps ahead of the person they're interacting with. ESTPs use this ability to get what they want out of a situation. Rules and laws are seen as guidelines for behavior, rather than mandates. If the ESTP has decided that something needs to be done, then their "do it and get on with it" attitude takes precedence over the rules. However, the ESTP tends to have their own strong belief in what's right and what's wrong, and will doggedly stick to their principles. The Rules of the Establishment may hold little value to the ESTP, but their own integrity mandates that they will not under any circumstances do something which they feel to be wrong.
ESTPs have a strong flair for drama and style. They're fast-moving, fast-talking people who have an appreciation for the finer things in life. They may be gamblers or spendthrifts. They're usually very good at story telling and improvising. They typically makes things up as they go along, rather than following a plan. They love to have fun, and are fun people to be around. They can sometimes be hurtful to others without being aware of it, as they generally do not know and may not care about the effect their words have on others. It's not that they don't care about people, it's that their decision-making process does not involve taking people's feelings into account. They make decisions based on facts and logic.