A Space Marine Dreadnought is a large, walking tank which carries both powerful guns and lethal close combat weaponry, armoured to withstand all but the most powerful of enemy firepower and often relied on by Space Marine forces to tear an opening in enemy defenses. Each Dreadnought contains a living being, permanently interfaced with the machine through a form of Mind Impulse Unit. Dreadnoughts are surprisingly agile, able to walk and balance with the ease of a living creature. It is said that old proto-Dreadnoughts of the Unification wars could be piloted by non-Adeptus Astartes warriors, but later only Space Marines could be interred in them.

It helps to give this one scale, as the source images are mostly miniatures or without other context - 4 meters is about right.

prompt: a four meter tall <color> drdnght machine <does things, usually angrily>