Harlen Tyrell

Harlen Tyrell was the steward of Highgarden during the reign of King Mern IX of the Reach. After the death of his king in the Field of Fire, Harlen surrendered Highgarden to Aegon the Conqueror. Afterward, Aegon elevated Harlen to Lord Paramount of the Reach and Warden of the South and House Tyrell to the status of a Great House.

In the books
In the A Song of Ice and Fire novels, Harlen Tyrell's story is the same