Eönwë was a Maia serving Manwë as his herald and banner-bearer, and Chief of the Maiar along with Ilmarë.
Eönwë was referred to as the "greatest of arms in Arda," meaning that he was the best with weapons, but as one of the Maiar he was not necessarily the most powerful in might. When Eärendil reached the shores of Aman to make his appeal, it was Eönwë who first greeted him outside of Tirion praising his arrival and accomplishments. When Manwë decided to heed the appeal, Eönwë was sent to Middle-earth to fight the War of Wrath, leading the Host of the Valar.
When Morgoth the Black Foe was defeated, Eönwë took the two remaining Silmarils and held them for safekeeping. The two remaining Sons of Fëanor took them and fled, yet Eönwë did not let them be slain hoping they would see the folly of their ways. After the War of Wrath, Sauron emerged from hiding and approached Eönwë seeking forgiveness, but Eönwë did not have the authority to pardon him alone, and told him he would have to return to the Valar to receive judgment, but Sauron fled from him instead.
Eönwë also possessed great wisdom and taught the remaining Edain many things, enriching them with great knowledge before the raising of Númenor.