Reverend William Miller (1782-1849) was comparable to other baptist preachers of the time during the Second Great Awakening. However, during the 1830s he partnered with Joshua V. Himes another well known and respected baptist minister. The two gained traction with the media and public as they began outwardly expressing thier views on the second comming of Christ. While the interpretation of christian scripture at the time was that Christ would come again to save beleivers, and condemn everyone else to eternal damnation, the time of this event was not clearified through scripture. This is why it was so polarizing for Miller and Himes to propose that they knew what day it would be, as well as being in thier near future. 

Ultimately looking back it is clear that these predictions were wrong, but Miller was wrong multiple times. The following he had created initially predected that the end would come on March 21, 1843. However Miller never confirmed this date, allowing himself to be more genrous by saying that it would be that year. However, this date and year would come and pass with no sign of an apocolypse. Miller would even predict some more dates before his final prediction of October 22, 1844. As the day came and went it became known as the, "Great Dissapointment". Even into his death Miller insisted that the endof the world they knew was close. 

Sources:

“The Millerites and Early Adventists, 1840-1870.” ProQuest, about.proquest.com/products-services/film/the-millerites-and-early-adventists-1840-18701.html.

Norwood, K. “Vermont Digital Newspaper Project (VTDNP).” Vermont Digital Newspaper Project VTDNP, Flickr, 21 Mar. 2015, library.uvm.edu/vtnp/?p=2765.