Viestards ( also Viesthard, Vesthardus, Viesturs) was one of the greatest Semigallian leaders in the 13th century, sometimes referred to as King of Semigallia. His capital was Tērvete. During the first decades of the 13th century he was allied with the Livonian Brothers of the Sword against Lithuanians, who looted Semigalia on several occasions. In 1205, joint forces defeated Lithuanians and killed duke Žvelgaitis.

When German crusaders broke the peace treaty and attacked the Semigallian castle in Mežotne, Viestards became an enemy of the Livonian Brothers of the Sword. He made an alliance with his neighbors, the Samogitians. Together they fought against the crusaders. Viestards died in 1230, but the Semigallians still were not conquered until the beginning of the 14th century. Viestards never accepted Christianity and accepted only one monk in Semigallia as a preacher.

The Order of Viesturs (Vesthardus Rex) was founded in 1938 to commemorate the spirit of independence of the people of ancient Latvia.