Ko'olau are a high quality ukulele maker from Wahiawa, Hawaii. All Ko'olau ukuleles are handmade in Hawaii which ensures their quality (and also the price tag to match). Their caliber is attested to by endorsements from players like Ledward Kaapana, Lyle Ritz and Abe Lagrimas Jr.
If you don't have the budget for a Ko'olau, you might like to check out Pono ukuleles - Ko'olau's (relatively) cheaper range of ukuleles.
Abe Lagrimas, Jr is one of many top class ukulele players who endorse Ko'olau.