This is General Grievous:

Durasteel. Ceramic armorplast-plated duranium. Electro-drivers and crystal circuitry. Durasteel.

Within them: the remnants of a living being. He doesn't breathe. He doesn't eat. He cannot laugh, and he does not cry.

A lifetime ago he was an organic sentient being. A lifetime ago he had friends, a family, an occupation; a lifetime ago he had things to love, and things to fear. Now he has none of these. Instead, he has purpose. It's built into him.

He is built to intimidate. The resemblance to a human skeleton melded with limbs styled after the legendary Krath war droids is entirely intentional. It is a face and form born of childhood's infinite nightmares.

He is built to dominate. The ceramic armorplast plates protecting limbs and torso and face can stop a burst from a starfighter's laser cannon. Those indestructible arms are ten times stronger than human, and move with the blurring speed of electronic reflexes.

~ A brief description of General Grievous and his cybernetic enhancements,"Star Wars: Revenge of the Sith novelization".

Usually a brilliant scientist, a sophisticated billionaire, or a superhuman being with advanced technology, this is someone who wears a mechanical suit or armor to upgrade an aspect of their body. This also includes villains who have replaced parts of their body with mechanical parts, i.e. cyborgs (examples include General Grievous and Darth Vader).

This category often coincides with Gadgeteers but differs by the fact that Gadgeteers almost exclusively use their own inventions whilst Mechanically Modified beings may utilize stolen technology (such as Apocalypse) and are usually dependent upon their advanced technology, without which they are severely weakened (unlike many Gadgeteers, who are smart enough to survive even without their "toys").