Richard I the Lionheart of England becomes the first European leader to take up the cross and agree to participate in the Third Crusade. He is not yet king — that won't happen until September 3, 1189 — but his father won't agree to go on a Crusade until January 21, 1188, when he and King Philip II of France learn of the fall of Jerusalem to Saladin.
Preparations will take a long time, and in the interim Henry II dies, leaving the leadership of the English part of the Third Crusade in Richard's hands. He will lead a force of 4,000 men-at-arms, 4,000 foot soldiers, and 100 ships. He achieves this by spending most of the treasury funds his father had built up over the years, raising taxes, and creating lots of new offices and titles to sell. It's said that he once declared that he'd sell London itself to help finance his expedition if he could only find a buyer.