Jaina Solo is a human female, daughter of Han Solo and Leia Organa, twin sister of Jacen, born in The Last Command (Bantam Spectra, 1993). Over roughly twenty years of Legends publishing she becomes the closest thing that shelf has to a second-generation lead.
Her father's daughter
Where Jacen is contemplative, Jaina is mechanical. She is a pilot before she is a Jedi, she flies with Rogue Squadron, and her instincts are those of a squadron officer — assess, commit, adjust. The New Jedi Order series puts her through a genuinely dark stretch in which she leans into a vengeful, predatory version of her power and has to be argued back from it.
Sword of the Jedi
Luke Skywalker names her the Sword of the Jedi in a formal knighting, a title that is meant as an honour and reads, in the books that follow, more like a sentence. It is the setup for the ending of Legacy of the Force, in which she is the one sent to stop her brother. The series does not soften what that costs her.
Legends only
Like her brother, Jaina exists only in Star Wars Legends. There is no canon equivalent. Her marriage to Jagged Fel and her role in the Fate of the Jedi series close out the Legends timeline's family saga.
Reading note
Jaina is the best argument that the Legends shelf knew how to write a sequel generation. Whatever you think of the sequel trilogy, the books got there first and took nineteen novels to do it properly.