The Angel Moroni is a figure that featured prominently in Latter Day Saints theology. He allegedly appeared to Joseph Smith, the founder of Latter Day Saints movement, and several other witnesses in 1800s. He was the guardian of the Golden Plates, which were believed to be the source material for the Book of Mormon. Moroni was believed to be a prophet of the native Americans prior to becoming an angel after his death.
Compared to other mainstream modern Christians, the Mormons reject the Nicene Creed of the 4th century and have additional scriptures, such the Book of Mormon and the Pearl of Great Price. They believed Jesus visited America and provided further revelations to the native Americans.
The name Moroni is subject to censorship by the incompetent word filter of Granado Espada game client. (The word moron is censored.) There is also a South Park episode that parodied the history of the Book of Mormon. You can watch the episode - All About Mormons - here.