Describe three characters in Jonathan Livingston Seagull.

Jonathan, the title character in the story, represents the individualistic human desiring to fulfill his personal search for perfection in the area that is important to him. For Jonathan, that field of endeavor was learning how to fly, in the ultimate sense of the act.

For most gulls, it is not flying that matters, but eating. For this gull, though, it was not eating that mattered, but flight. More than anything else, Jonathan Livingston Seagull loved to fly.

Being rejected as Outcast from the Flock was not a concern; the important thing was continuing the search for knowledge about the science and application of advanced flight, as shaped by the body of a seagull.

The Elder Gull, Chiang, serves as a metaphor for God, teaching Jonathan lessons that included the mechanics of flight but went beyond them to encompass the philosophical applications of the knowledge to serve his own purposes and to allow him to help others.

The trick, according to Chiang, was for Jonathan to stop seeing himself trapped inside a limited body...The trick was to know that his true nature lived, as perfect as an unwritten number, everywhere at once across space and time.

Fletcher Lynd Seagull becomes the first of Jonathan's pupils when Jonathan returns to the beach and the Flock. Fletcher has the same hunger to learn about flight as Jonathan did, but is angry about the  rejection of the others. Jonathan's curiosity and desire to learn consumed all his energy; Fletcher needs to be forced to admit that his judgemental attitude harms only himself. The way for Fletcher to learn to fly starts with him learning to forgive.

Fletcher Lynd Seagull, do you want to fly so much that you will forgive the Flock, and learn, and go back to them one day and work to hep them know?"..."I do," he said softly.

Who are the main characters in "Jonathan Livingston Seagull" besides Jonathan?

The story of Jonathan Livingston Seagull centers primarily around the title character. There really are not any other main characters. There are a few other characters that are significant in telling his story and who are worth mentioning.

One such character is Elder Gull. He is the leader of the flock's council. He represents an older conservative viewpoint that has no predilection or appreciation for experimentation and pushing limits. It is he who banishes Jonathan from the Flock.

Old Chiang, otherwise known as The Great Gull, is an old and sagacious bird who instructs Jonathan on the true meaning of life and how to transport himself anywhere in the universe with a mere thought. Love, old Chiang tells Jonathan, is the highest of all achievements. This is not just the love of others, but also the love of oneself. In many ways, Old Chiang is a stand-in for the divine. He is a repository for all the knowledge and wisdom of the universe.

Fletcher Lynd Seagull is one of Jonathan's main pupils after he returns to his old flock. Fletcher believes that flying is a gift that is to enjoyed and taken to its greatest limits. As a result, he is cast out of the flock. Fletcher is keen to learn the lessons that Jonathan has to teach him. Fletcher is young and eager. He also has a developed sense of justice. Fletcher is an apt learner who takes Jonathan's lessons to heart. However, he remains judgemental of the flock that made him an outcast. His greatest struggle is learning to forgive his old companions.

Martin William Seagull is a lesser but still important character. He is one of Jonathan's other pupils. Though crippled, he learns to fly expertly at low speeds under Jonathan's tutelage.

Jonathan is described in the link referenced below as the only true major character in the book.  The other characters are all considered to be minor characters, and more or less thematic stereotypes.  Old Chiang is wise and mystical, Fletcher Lynd Seagull is young and eager, and Martin William Seagull is a cripple who overcomes his handicap through the power of his mind and learns to fly.