The Four Horsemen of the Apocalypse ~ Bob Thiel

What do each of the four horseman of the Apocalypse represent? Have they began their ride? Did Jesus discuss the any of this? Might their rides coincide with the "beginning of sorrows? Do they start their ride prior to the Great Tribulation? Did Nostradamus or any other 'private prophets' write predictions that may mislead people so that they may not understand the truth of one or more of the four horseman?