Brona the Warlock Lord is the principal villain of Terry Brooks' novel The Sword of Shannara.
The Warlock Lord was formerly the Druid Brona. He desired power, and delved deeply and quickly into forbidden knowledge and was corrupted by the dark power of Ildatch, a book of magic said to have a mind of its own. His first attempt to subvert The Four Lands resulted in the First War of the Races, in which he led an army of Men. He and his followers were defeated by the combined forces of the other races, led by the Druid Council. Brona was never found and presumed dead.
His second appearance occurred during the time of Jerle Shannara, this time as the spirit called the Warlock Lord. He marshalled an army of Trolls and Gnomes in secret in the Northland, and slaughtered the Druids at Paranor in order to assure his success. Jerle was given the Sword of Shannara by the Druid Bremen, one of the few to survive Paranor, and with its power he defeated the Warlock Lord. But because he doubted himself, he could not unleash the Sword's full power, and Brona's spirit survived and fled.
Several hundred years later, it quickly becomes apparent he still existed, marshalling his evil forces to once more make war on the Four Lands. He sent his Skull Bearers to seek out and slay all descendants of the Shannara line, as they were the only ones who could wield the sword that had nearly destroyed him centuries earlier. Because The Warlock Lord did not initially know that Shea Ohmsford even existed, Shea was the last one alive.
The Druid Allanon came to Shady Vale and warned Shea of the impending danger, and eventually Shea and his brother Flick fled from their home when a Skull Bearer came hunting for Shea. Shea later recovered the Sword of Shannara, which had been stolen by the Warlock Lord's minions, and the descendant of the house of Shannara came face to face with the Warlock Lord.
Until that point, Shea had not known exactly the true power of the sword. However, upon wielding it, he realized the sword's only power was to reveal to those who touch it truths about themselves. After struggling with his own inner demons revealed to him by the sword and against the mental assaults of fear from The Warlock Lord, Shea finds the strength to strike him with the sword.
Because the nature of the Warlock's sorcery was based on belief, Brona had kept himself alive for hundreds of years through denying his own death. The Sword was able to destroy him by revealing to him the truth of his existence, that for all his awesome power he was, in fact, quite dead.
When Grianne Ohmsford is trapped in the Forbidding several hundred years later, she comes upon a darker version of the Hadeshorn where the malevolent spirit of Brona is bound for eternity, like his Druid counterparts back in the Four Lands. Although he is angered at being summoned, he does not attack Grianne, and in fact offers her advice on what to do before returning to his rest under the Hadeshorn.