Most powerful commoner

[Emperor Demonking]

The character can only have leves in commoner up to level 20.

1) Most perful cr20 commoner, phb races plus anything else no limit.
2) Most powerful cr 20 commoner, no limit on races.
3) Most powerful commoner.

[Hazkali]

Well, obviously (2) will be an ECL 19 monster with two levels of commoner... I can't think of an appropriate race at the moment, but I'm sure there are Celestials or Fiends that fit the bill.

[vrellum]

It will be hard to fulfill the requirements for #1. I believe a 20th level commoner is a CR 10 challenge. Using only PHB races I don't think there is any way to create a CR20 commoner using only 20 levels in commoner.

[Emperor Demonking]

You can add templates.

[Reinboom]

Stats?
Do you mean ECL 20? If so...
1)
Race- Doesn't matter.
Stats focused on Charisma and Con.
Feats:
Skill Knowledge (Use Magic Device)
Magical Aptitude
Skill Focus (Use Magic Device)
Improved Toughness
The 3 save boosters. (7 feats)

Skills:
Use magic Device

[vrellum]

don't forget leadership for all of the options.

A 20th level commoner with maxed out UMD and an 18th level codzilla or wizard or artificer cohort would be pretty tough.