"This hulking, powerfully built creature looks something like a cross between a great ape and a beetle. The low, rounded head is dominated by a massive pair of mandibles and rows of triangular teeth. It has two big compound eyes like a beetle's, with two smaller eyes like an ape's in between. Armor plates cover virtually all of its chitinous body, whose scattered feelers resemble sparse hair."
Umber hulks look somewhat like a cross between a gorilla and a beetle. Their most prominent feature is probably the huge pair of mandibles, each roughly as tall as a halfling. Four eyes, one pair multifaceted, the other seemingly normal allow it to both see in the darkness in which it lives and somehow befuddle their enemies with merely a look. Their massive claws tunnel through rock with ease and it's thick armor is as strong as full plate mail.
Most people seem to think that umber hulks are unthinking brutes. This is simply not the case. They can communicate in Terran and often create traps using their digging abilities. Umber hulks tend to choose to collapse the tunnels they leave behind, so as to prevent access to where they had just tunneled. That being said, they care not for subtlety, creating much destruction wherever they go and can often be found dominated by illithid for use as dumb muscle.