The Sukhoi Su-33 (NATO reporting name: Flanker-D) is an all-weather carrier-based air defense fighter designed by Sukhoi. It is a derivative of the Su-27 "Flanker" and was initially known as the Su-27K. The aircraft was first used in operations in 1995, aboard the carrier Admiral Kuznetsov. It officially entered service in August 1998, by which time the designation "Su-33" was used. Following the break-up of the USSR and the subsequent downsizing of the Russian Navy, only 24 aircraft were produced. Attempted sales to China and India fell through.
Compared with the Su-27, the Su-33 has a strengthened undercarriage and structure, folding wings, and stabilators, all for carrier operations. The wings are larger than on land-based aircraft for increased lift. The Su-33 has upgraded engines and a twin nose wheel, and is air refuelable. The aircraft's range and payload are greater than those of the rival MiG-29K, but the Mikoyan fighter has more advanced avionics and is capable of a wider range of missions, including strike operations. In 2009, the Russian Navy ordered the MiG-29K as a replacement for the Su-33.
Source: Wikipedia, "Sukhoi Su-33", available under the CC-BY-SA License.