The Canon Pellix came out in 1965, and even though it doesn't have the letter in its name, it's part of their F-series cameras. It was the third in the series (behind the FX and FP), but the first to have through-the-lens (TTL) metering.
It got its name (very few Canon SLRs are named, most get number or letter designations) from the "pellicle" mirror inside, which is what made the camera unique. SLRs work on the principle that the photographer sees the same image that passes through the taking-lens, so what you see is what you get. This is accomplished by putting a mirror at a 45° angle between the rear of the lens and the shutter. The mirror has a hinge and a spring mechanism that lifts it up and drops it back into position. When focusing and composing, the mirror is down and the photographer and set up the shot. When he fires the shutter, the mirror swings up and out of the way, the shutter opens, and light can pass directly from the lens to the film. Then the shutter closes and the mirror drops back down into position. Pretty much all SLRs, even my old Graflex, use this principle.
There are a bunch of drawbacks to this arrangement, however. First is that when the mirror swings up out of the way, the viewfinder goes dark and the photographer can't see anything until the shutter is fired and the mirror drops back down. On fast shutter speeds the dark time is short, but with longer shutter speeds the dark time is annoyingly long, so the photographer is never 100% certain what he shot. Then there's the the fact that the mirror action is very loud. Cameras with leaf shutters are typically very quiet and discreet, but SLRs clatter when the shutter fires. Part of it is the shutter, but some of it is the mirror.
So Canon experimented by putting in a beam-splitting, stationary mirror. Part of the light bounces up through the viewfinder, part passes back to the film plane. The mirror never moves so there's no vibration, no clatter, and especially no black-out when the shutter fires. Great idea.
But it didn't catch on. Beam-splitters mean less light goes to the viewfinder, which makes focusing harder and the image less crisp, and it means slower shutter speeds or larger apertures for exposure. The camera sold but not enough to incorporate the feature into later models (though it's now used in the modern high speed EOS cameras, where shots can be taken much faster because you don't have to wait for the mirror to flip up and down, or have dark-time while the mirror is up.
I got a black-bodied version, which I think is rare: Pellixes were not big sellers in any style, and I didn't know they'd made a black-body variant at all until I saw the one I bought.
Now Canon actually considers that there are two different Pellix cameras, the first version and the QL version; mine has the QL badge so it's obviously the latter. Canon did that a lot with various cameras. The main difference is that mine has the quick-load QL feature, which is nice. I'm told that it is also has some changes to accommodate Canon's Meter Booster (which I don't yet have).
One last comment: there are two other things that make this camera very unusual for a Canon product: the first is that it's named (Canon often named its rangefinders or point-n-shoots, but almost never named its SLRs). The other is the location of the name. Almost all Canon cameras have the Canon name on the prism (in the center of the camera over the lens) and the model designation on the camera's right-hand side (on the left if you're viewing it from the front). But the Pellix has the name on the prism and the Canon logo on the side. You wouldn't see that again until the T-series cameras (like the T-70) came out twenty-years later—and even then the Canon logo stayed on the prism.
For more information: Canon Camera Museum
Modern Photography magazine camera test: August 1966
Modern Photography magazine "Camera Collector" article: September 1980