Tale of Diep:The Veil

The Veil was a Son of Panzer who ruled the city-state of Arena during The Old Era, before tanks came in and conquered it, pushing him and his regime out. He died near the end of The Old Era, never being revived by Panzer because he was unaware of the war The Veil started until nearly ten millennia later. Panzer considered him an unnecessary burden. He was the Boss Tank variant of a dead tank type never formed into a weapon by the Tank Empire that followed pushing him out of Arena. The tank based off of him was nicknamed the X-Hunter.

History
The Veil was given control of a weak city-state on the outskirts of the realm known as Arena, and ruled it with an iron fist. He was considered the weakest and stupidest of the Sons by the general tank population at the time. This all occurred during the early part of The Panzer Era.

When The Old Era began, hordes of escaped tank slaves ran in and brought siege to the city, conquering it and throwing The Veil out for thousands of years, before he returned with an army in the tens of millions. The Tank Empire held out for 1000 years, before the final battle at the heart of Arena, where The Veil was shot down and killed. Panzer might have revived The Veil had he known this war had even happened. That might have prevented the Great Dark One's downfall, as he would have discovered Tank society sooner and would have easily wiped them off the face of the realm before they could muster the ritualists to seal him away.

Ten millennia later, Panzer discovered the Tank Empire and found out about the death of his son. He chose not to revive him because of his general stupidity and lack of cooperation. So... he never came back, and tanks never developed a Level 45 weapon based after him. The same happened to another son, The Pulverizer, whose original form was nicknamed the Mega Smasher. He had done so little, no archive even contains records or information on this forgotten smashing Son.

Trivia

 * Only listed unfightable Son of Panzer.
 * The Pulverizer mentioned in page was ACTUALLY going to be a Boss Tank before they removed Mega Smasher from the game. X-Hunter had a different name as its original Boss Tank concept, but I like this new name.