Lowbacca — Lowie to everyone who knows him — is a Wookiee from Kashyyyk and Chewbacca's nephew, introduced in Young Jedi Knights: Heirs of the Force (Berkley Jam / Boulevard, 1995), the first of the fourteen-book Legends series by Kevin J. Anderson and Rebecca Moesta.
The character exists to answer a question the Expanded Universe kept circling: what does a Wookiee Jedi look like? The answer the books give is not "an angrier Chewbacca". Lowie is a computer specialist who carries a translator droid, builds his own lightsaber with a Kashyyyk gemstone, and spends most of the series being the technically competent one while the Solo twins improvise.
He carries through the New Jedi Order series into adulthood — fighting the Yuuzhan Vong, losing people, becoming a Knight — and is one of the few Young Jedi Knights cast members the adult novels treated as a serious asset rather than a nostalgia cameo.
All of it is Legends. Current canon has Wookiee Jedi of its own, notably Burryaga in The High Republic, but Lowbacca was there first by twenty-six years.
