The HEMI was the shape of the combustion chambers of some of the most powerful and successful Chrysler engines in the '70s, the most notable one being the 426. The shape was in use long before Chrysler came up with it; the earliest HEMIs can be found in engines built in the '20s.
Now, the HEMI is proof that brand name affinity sells cars, and that nothing in the automotive industry is sacred. The current design is a ripoff of a Porsche design. If you want to visualise what the current HEMI head looks like, take a pear, cut it in half lengthwise, and lie it down. The big circular section is where the intake valve is, and the small one is where the exhaust valve is. The TWO spark plugs reside at the "waist" of this pear-shape, one on each side. Note that there isn't two plugs for added performance, but rather because one plug off to the side couldn't hope to burn all of that fuel.
I park my Dodge Ram with the HEMI right next to my new Olds 4-4-2 minivan and Ford Escort Boss 429.
Damn, I wish someone told me that this HEMI crate engine weighed 5000lb and is only suitable for drag racing.