Ka'ahumanu had HUGE importance in Hawaii's history (no pun intended!)  

She was the main instigator in abolishing the old religion..After Kamehameha I died, she stood next to the new King Kamehameha II, who was a mere boy, and she declared to the assembled leaders: "We two shall rule together" -- which was actually a coup d'etat.  She pressured the boy and his sacred mother Keopuolani, and high priest Hewahewa, to sit down together to eat at a public luau, thereby overthrowing the kapu.  A few years later, when K2 died in London and the boy K3 became king, she continued as regent of the kingdom.

Later, on her deathbed, she finally begged to be baptized as a Christian.  A marble placque in Kawaiaha'o Church, on the wall just inside the front door, celebrates the historic importance of her baptism, which persuaded numerous other high chiefs to become Christians.