MOHAMED THE WARLORD
The vast majority of the religious leaders through history have been peaceful. Jesus Christ told his disciples that if someone "smites you on the right cheek, turn to him the other also."
The bizarre exception to this norm, however, was the founder of Islam. Mohamed was not just a violent man, he was a conquering warlord who spread his religion with the sword.
Mohamed's ambition led him to violently conquer the cities of Mecca and Medina, and lead countless raids on Arabian caravans. By the time of his death, in AD 632, Mohamed had become the warlord of the entire Arabian Peninsula. 
These many conflicts led to thousands of deaths.
In one of many brutal incidents of Mohamed's violence the warlord personally ordered his troops to rape conquered women in front of their husbands. This is recorded by Mohamed's companion in the Hadith:
"They met their enemy and fought with them. They defeated them and took them captives. Some of the Companions of the apostle of Allah were reluctant to have intercourse with the female captives in the presence of their husbands who were unbelievers. So Allah, the Exalted, sent down the Quranic verse, 'And all married women (are forbidden) unto you save those (captives) whom your right hands possess.'" Such a disturbing atrocity surely discredits the prophet of Islam, and casts doubt upon the moral integrity of those willing to follow him.
Mohamed was a racist who hated Jews. In one particularly disturbing incident the "holy" prophet decided to commit genocide against a Jewish tribe called the Banu Qurayza. He accused the entire tribe of treason (without evidence), ordered his men to dig a giant hole in the middle of their town, and then personally decapitated between 700 and 900 men and elderly women. 
After slaughtering all the males, he divided the remaining women and distributed them among his men as sex slaves. He took a women named Raihana bint Amr as his concubine, right after he severed her husband's head. 
The prophet Mohammad was a pedophile.
This may come as a shock to those who were taught that Islam's founder was a great moral teacher. Nothing could be further from the truth. At the age of 51 Mohamed married his 6 year old niece Aiesha. Modern Muslims rush to point out that he didn't consummate the marriage until she was 9, as if that justified it. 
This pedophiliac marriage was among the most well documented events of Mohamed's life.
Even by the standards of the somewhat backward Arabs, Mohamed's desire to marry the girl was considered incestuous. In fact, Mohamed had to receive a special revelation from Allah in order to convince the girl's father to allow it. 
 Muhammad 2014. Encyclopædia Britannica Online. Retrieved 17 January, 2014.
 Hadith Sunan Abu Dawud 2:2150 (see also: Quaran 4:24)
 Azumah, John. 'My Neighbors Faith: Islam Explained for African Christians.' Zondervan. 2008.
 Peters, F. E. Mohamed and the Origin of Islam. Page 222-224. State University of New York Press. 1994. "Then he [Mohamed] sent for them and struck off their heads in those trenches as they were brought out to him in batches."
Aisha herself testifies to her age when the consummation took place in Sahih Bukhari volume 5, book 58, number 234.
 The girl's father was one of the Hadith's writers. His account can be found in Sahih Bukhari 7.18: "The Prophet asked Abu Bakr for 'Aisha's hand in marriage. Abu Bakr said' But I am your brother.' The Prophet said, 'You are my brother in Allah's religion and His Book, but she (Aisha) is lawful for me to marry."