Telemon Heavy Dreadnought

A Dreadnought so huge you will mistake it for a Knight.
One day the Emperor thought: "How am I going to stop some big mean Xenos abomination from tearing my Golden BFF's a structurally superfluous new behind? The answer, use a gun. And if that don't work use more gun.

The Adeptus Custodes Telemon Heavy Dreadnought is a heavy duty variant of the normal Custodes Contemptor-Galatus Dreadnought. Essentially, the Custodians felt a bit left out in the Super-heavy walker department. The Elfdar has one of the most ridiculously broken walkers in 7th Edition, the Weeaboos have their annoying Supremacy Armour to reenact Gundam, the Orks still get to play around with their twin walkers which prevents them from being shitcanned into irrelevancy like the Nids, the Grey Knights was still able to keep their infamous baby carriers whilst the rest of the Imperium gets to roleplay in medieval dress ups in the form of the Imperial Knight.

The Emprah in all his infinite wisdom said to himself, "I can't let my golden bros be left out! They need to be better in every way!" Thus, the Telemon Heavy Dreadnought was born. A walker so ridiculously large and bulky that some have mistaken it for an Imperial Knight (understandable since it's the same size as an Armiger Knight). No Dreadnought even came close to the sheer size and firepower this thing brings on the battlefield. Even the ridiculously bulky Leviathan Dreadnought looks like a Dorf in comparison. The Heavy Dreadnought is used as a Super-heavy fire support weapons platform that can perform a number of various roles on the battlefield. It can act as a close combat wrecking ball with its two oversized Powerfists simply called the Telemon Caestus with an in-built wrist-mounted Plasma weapon called the Proteus Plasma Projector which is essentially a giant middle finger to all horde armies who thought they could overwhelm the Telemon in close combat. It can also perform as a dedicated tank hunter by swapping one of its arms with a twin-linked Gatling-Lascannon Array called the Arachnus Storm Cannon (Yep, this thing has a giant gatling gun that uses Lascannons as its barrels), or a heavy infantry destroyer with the Iliastus Accelerator Culverin. All of them have an oversized Cyclone Missile Launcher called the Spiculus Bolt Launcher for when you want to soften up resistance and flatten the landscape. The Telemon is by far one of the most versatile and powerful ranged unit/vehicle in the Adeptus Custodes. Subtlety and modesty is often the first victim when these golden Goliaths start walking over the battlefield.

Mandatory "learn Ancient Terra's history and myths with Professor Custodes" part : we can assume that the Telemon Dreadnought is named after Telamon, a legendary Greek king, one of the Argonauts, and father of the hero Ajax.