Star Wars: The Thrawn Trilogy - Legends (abridged)

Heir to the Empire begins five years after Return of the Jedi. The Rebel Alliance has destroyed the Death Star, defeated Darth Vader and the Emperor, and driven the remnants of the old Imperial Starfleet back into a quarter of the territory it once controlled. But thousands of light-years away, the last of the Emperor's warlords have taken command of the remains of the Imperial fleet - and have made two vital discoveries that could destroy the fragile new Republic.

The dying Empire's most cunning and ruthless warlord, Grand Admiral Thrawn, has taken command of the remnants of the Imperial fleet and launched a massive campaign aimed at the New Republic's destruction. With the aid of unimaginable weapons long hidden away by the Emperor on a backwater planet, Thrawn plans to turn the tide of battle, overwhelm the New Republic, and impose his iron rule throughout the galaxy.

The embattled New Republic reels from the attacks of Grand Admiral Thrawn, who has marshaled the remnants of the Imperial forces and driven the Rebels back with an abominable technology recovered from the Emperor's secret fortress: clone soldiers.