The Klingon Empire is a race of warriors. They're whole civilization is based on honor and courage and fighting to the death. They have strong ships, and strong bodies. To die in battle is a great honor. A famous Klingon saying, that comes from the first true Klingon warrior, Kahless, is "It is better to die on foot, than to live on your knees." In the Original Seriers, the main Klingon was Kor. In DS9, the main Klingons were Worf, Son of Mogh, Martok, who later became chancellor of the Klingon High Command, Gowron, who reigned for quite  a while before getting killed by Worf. Some Klingons have been known to be treacherous, such as the illusive Duras family.
The Klingons have a very rich and honorable culture, and can be very blood thirsty, always fighting to the death. The Klingons have been in numerous wars. They have fought the Federation numerous times, the Romulans, and the Dominion. They were the third race in the Federation Alliance against the Dominion, along with the Romulans.