Dauntless (The Lost Fleet, #1) by Jack Campbell

The Alliance has been fighting the Syndics for a century–and losing badly. Now its fleet is crippled and stranded in enemy territory. Their only hope is a man who’s emerged from a century-long hibernation to find he has been heroically idealized, beyond belief…

Captain John “Black Jack” Geary’s legendary exploits are known to every schoolchild. Revered for his heroic “last stand” in the early days of the war, he was presumed dead. But a century later, Geary miraculously returns from survival hibernation and reluctantly takes command of the Alliance fleet as it faces annihilation by the Syndics.

Appalled by the hero-worship around him, Geary is nevertheless a man who will do his duty. And he knows that bringing the stolen Syndic hypernet key safely home is the Alliance’s one chance to win the war. But to do that, Geary will have to live up to the impossibly heroic “Black Jack” legend…