Who is Charles-John Austen from Jane Austen's Letters and what is their importance?

Charles-John Austen, born on June 23, 1779, was educated at the Royal Navy Academy from 1791 to 1794. He married Frances-Fitzwilliam Palmer on May 19, 1807, and the couple had four daughters. After his wife's death, he married her sister, Harriet. They had three sons and one daughter.