The Free Dictionary provides a definition of “beetle-browed”:
[Middle English bitel-brouwed , having grim brows, sullen, perhaps from bitil, betil, bug, beetle (from the resemblance of a pair of thick eyebrows to the tufted antennae of a cockchafer); see beetle1, or from bitel, sharp (probably from Old English *bitol, biting, from Old English bite, bite); see bit2 + brouwed (from brow, brow; see brow).]
Beetle-browed villains in comic books visually convey malevolence through a deep scowl. The remarkable similarity between some of these characters, though, extends beyond their visages. These villains also are very heavy-set, often donned in armour, frequently (but not exclusively) capable of projecting explosive forces from their hands, are alien, and seem born to rule. The examples we have listed below are the most obvious.
In the images below, we have deliberately not identified which character is which and modified the images to greyscale. The similarities are remarkable.