The Underground Railroad was a network of people, African American as well as white, offering shelter and aid to escaped slaves from the South. It developed as a convergence of several different clandestine efforts. The exact dates of its existence are not known, but it operated from the late 18th century to the Civil War, at which point its efforts continued to undermine the Confederacy in a less-secretive fashion. 
So, who created it? Well, it depends on who you ask. Some historians credit white Christian abolitionists - “the Quakers.” Quakers are a historically Christian denomination whose formal name is the “Religious Society of Friends” or “Friends Church.” Members of the various Quaker movements are all generally united by their belief in the ability of each human being to experientially access the light within, or “that of God in every one”.  The “Friends” were informally known as Quakers because they were said to “tremble in the way of the Lord.” 
Quaker leader George Fox, after a trip to Barbados, where he saw conditions slaves endured, pleaded with members of his sect to release their slaves even though they had treated them well. Not only did many Quakers release their slaves, but they saw to it that they could take care of themselves, teaching them to read and write and, in many cases, seeing that they were escorted to states or territories where they could live in freedom. 
Although George Washington freed all his slaves in his will,  he once complained that Quakers had attempted to “liberate” one of his slaves in 1786.