What in the World is a 454 Hemi?

We stopped for gas at a local station yesterday in our late model Challenger. The guy filling up next to us asked if the car was one of "them Challengers". I said yes. He proceeded to tell me his dream car is a 69 Charger RT. he would eventually find one with a good body and interior - no motor needed. He said he already had a motor for it - you guessed it - the famous 454 Hemi! Luckily, I finished gassing up about that time, told him good luck in his search and left before I cracked up laughing.