Whenever a cave man is depicted in media, he will often be The Big Guy, having more muscles and stature than his descendants. This is especially true if he's a regular character who has somehow been de-evolved, but usually it's a defrosted Human Popsicle scenario. They're typically rather unintelligent or at least simple-minded, and highly unsophisticated on a technical level — most will be (sometimes literally) knuckle-walking brutes who speak in a vocabulary-deprived Hulk Speak, clad in primitive animal pelts and fighting with simple Primitive Clubs. The may have just mastered a haphazard control over fire, and the brighter specimens may be all abuzz about new and experimental technologies such as the wheel.
Cave women, in the rare cases where they appear, are usually matronly and physically stronger than their modern counterparts, sometimes up to a Brawn Hilda-type, unless they're just here for Fanservice in which case they're Nubile Savages.
This is usually a case of poor research; the author is basing the caveman, not on the Cro-Magnons (the first generation of anatomical humans to inhabit Europe), but on the Neanderthals, who were stockier and likely stronger, but still shorter than Cro-Magnon man. It's almost as if in fiction humanity evolved from the Frazetta Man. The trope was invented by the fact that one of the first prehistoric skeletons was of a heavily arthritic old man with osteoporosis. Scientists mistakenly assumed he was the norm and not an outlier.
This may even extend to showing these super-ape-men as having Super-Strength, being incredibly athletic and acrobatic, and generally being savage fighters; which isn't quite so preposterous for a number of reasons.
Just for the record, compared to modern man (Homo sapiens sapiens), the Neanderthal man was either a separate species (Homo neanderthalensis) or a subspecies (Homo sapiens neanderthalensis), probably depending on who you ask. They evolved in Eurasia while we evolved in Africa). While closely related to modern humans, it's believed that they were not our ancestors, except perhaps in a small way — evidence from the Neanderthal Genome Project shows that interbreeding occurred between Neanderthals and H. sapiens in The Middle East 80,000 to 50,000 years ago, while in Europe, interbreeding is also believed to have occurred, as populations of modern humans and Neanderthals coexisted for around the same time. Most Caucasians and Asians seem to have a bit of Neanderthal DNA, while people of entirely African descent have none because there were never Neanderthals in Africa, while Polynesian and Oceanian DNA shows signs of interbreeding with a different close relative of humanity, the Denisovans, as the Neanderthals never ranged that far eastward. Since the Neanderthals were hardier than Cro-Magnons, there is evidence that they were better at handling certain common illnesses endemic to temperate and colder climates, and interbreeding transferred genes that are of direct benefit to the functioning of our immune system.
There is a practical aspect to this trope. This is often simply a result of the fact the easiest way to depict a caveman on Live-Action TV is to add brow ridges, fake hair, animal skin clothing, etc., to an actor, so the resulting Rubber-Forehead Alien will be slightly larger than a human, and rather large actors are often cast in the part.
This is usually a double case of artistic liberties — most often, Neanderthal cavemen are depicted as nothing but simple, dumb brutes capable of barely a grunt. The various sciences researching them indicate that this is untrue, too — in fact, they had larger brains than humans, although that extra brainpower was directed to different functions than in a modern human.note They were creative enough to know how to make glue from pitch and to make clothing and art, conducted funerary rituals similar to early modern humans, and used a complex technique for making tools called Levallois and later Mosterian, which modern humans also used at the same time. Considering they had to endure Arctic-level conditions, they really weren't dumber than modern humans, just different.
Even visually, the divergence between Neanderthals and modern human is often exaggerated too. Far from hulking, inhumanly-proportioned monsters, Neanderthals weren't that scary-looking; if you dressed one of them in modern clothing and put him among the passengers in a subway car, pretty much nobody would notice him.
Contrast: Nubile Savage, where prehistoric men will be hulking, ugly brutes, but prehistoric women are pinup models with bodies that exactly correspond to the current standards of beauty, and Handsome Heroic Caveman, where the man will be more attractive to go with a more modern sense of morality. For more bestial humanoids, check out Frazetta Man. Even earlier than these guys are Original Man.
