Let's break down the facts behind two of the most famous leaders the world has to offer, shall we?
Here are 5 Reasons why Warmaster Seerus is actually King DeDeDe. I'm being D-D-Dead Seerus here, folks ;d

1: Both command an army of minions proficient in battle.

The King and the Warmaster possess total control over a countless army of lesser beings, who have many roles in their militia, from footsoldiers, to demolition experts, to engines of war.

This amassment of sheer military prowess mirrors the Grand Arsenal's army precisely.

2: Weapon of choice.
The Hammers of both characters in question have one distinguishing feature: the rocket engine attached to them. This weapon choice alone is a relatively-unique feature in video games as a whole, and the staple of the two characters this thread is focused on.

3: Distinguishing mask:
Both tyrants sport a signature Mask worn in times of battle, giving them a fearsome visage that only reveals their eyes. When defeated, this mask breaks apart, leaving itself behind as the owner mysteriously vanishes.

4: Both answer to a higher power of unknown magnitude.
Seerus is a member of the Crimson Order, a circle of nine Gremlins who answer to a leader shrouded in dark mystery, King Tinkinzar.
King DeDeDe obtains his power and resources from Nightmare Enterprises, a powerful cosmic force that very little is known about other than the fact that its goal is conquest and war through sending numerous monsters to Dreamland from an unknown source.

5: They are both very intelligent in design of war machinery.
Seerus is named as the designer of the Twins and countless other war machines.
However, the King of Dreamland has a large arsenal of war robots as well, namely the Waddle Dee Tank, the DeDeDe Tank, the OTHER DeDeDe Tank, and Kabula, Flying Fortress.

These machines have brought down any and all opposition to the King's absolute rule.

Well, there it is, folks. Irrefutable proof that Warmaster Seerus is, in fact, the King of Dreamland.
Hail your new overlord, Knights.