https://www.looper.com/1011293/the-rings-of-powers-earendil-explained/

Eärendil recruited the Valar and helped save Middle-earth from Morgoth

Eärendil is the father of Elrond and Elros and the husband of Elwing. However, his legacy in Middle-earth goes beyond boasting an impressive family. During his lifetime, Eärendil was a half-Elven mariner who was instrumental in defeating Morgoth and his evil minions during the First Age. But how exactly did he manage to accomplish such a feat?

In short, Eärendil and Elwing sailed to Valinor and convinced the Valar to help aid Middle-earth in the war against Morgoth. Due to his half-mortal lineage, Eärendil was the first mortal to ever step foot on Valinor, which would usually have resulted in punishment. But his plea was so convincing that the Valar granted him immortality as an Elf instead.

Afterward, the Valar traveled to Middle-earth and defeated Morgoth in the "War of Wrath." Eärendil also took part in the battle, conquering the Dark Lord's most feared dragon, Ancalagon the Black, in the process. His war efforts made him a legend in Middle-earth, and he inspired future generations to follow in his heroic footsteps.