Thanos (Marvel)

What makes Thanos a Dark Lord either in comics or MCU?

I know the title main antagonist in Marvel and DC Comics is shared by their most evil and impactful villains (Thanos, Red Skull, Doctor Doom, Galactus)/(Darkseid, Lex Luthor, Joker, Sinestro), but is there any way to determine character(s) who could be "Secondary Antagonists" of the verses? Or are they just too expansive to do so?

1. Megatron (Transformers)

2. Frieza (Dragon Ball)

3. Madara Uchiha (Naruto)

4. Yhwach (Bleach)

5. Shao Kahn (Mortal Kombat)

6. M. Bison (Street Fighter)

7. Shredder (TMNT)

8. Heihachi Mishima (Tekken)

9. Thanos (Marvel)

10. Darkseid (DC)

Note: Y’all can put down your Top 10 Lists of your All Time Favorite Main Villains/Antagonists as well.

Sorry I was gone for so long