Born in 2940 3A, Haethen grew up in Rohan and began to learn all the strategies in becoming soldier. He was very careful in learning all steps and became a skilled fighter. In an unknown year, Haethen fought alongside his wife, who was also a soldier, against the Dunlendings. After his wife was slain in battle, Haethen grew enraged and slew any Wild-men that crossed his path until he was badly injured. The right side of his eye was removed, but Haethen recovered months later. Haethen continued to serve in the army and many soldiers called him "One-Eye". Haethen endured the name and kept it as his nickname.
During the War of the Ring, Haethen travelled to Helm's Deep where he escorted four hundred villagers from Snowbourn. He later participated in the Battle of Helm's Deep where he commanded hundreds of archers to fire upon an army of 20,000 Uruk-hai. Haethen fought valiantly in the battle and killed many Uruk-hai that were breaching the fortress. He was soon killed when a Uruk-hai plunged its spear into his chest, but he immediately decapitated his foe and tumbles slowly to the ground. After his death, he was buried along with those that perished during the battle. Théoden mentioned his name and called him a hero for defending the people he cared about.