Googled Fred the Diplomancer and I found him
Warning, long post.
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Race: Venerable Magic-Blooded Half Elf Alignment: Chaotic Good
Flaws: Inattentive, Noncombatant
Traits: Polite, Honest

Level Class Feat(s)
1 Half Elf Bard Substitution Level 1 Sacred Vow, Negotiator, Extra Music
2 Marshal 1
3 Bard 2 Item Familiar
4 Warlock 1
5 Cleric(evangelist option) 1
6 Half Elf Paragon 1 Leadership, Complementary Insight(B)


Stats of Importance:

Charisma: 18
Intelligence: 16 or higher
Dexterity/Constitution: Generically good for any character.

Equipment:

Wendsday's Left Eye (6,000gp)
Ring of Diplomacy +8 (6,400gp)
Mwk Diplomacy Tool [makeup kit] (500gp)
Anything Else (100gp)

His cohort must have at least 9 Wisdom, 11 Intelligence, and 18 Charisma before age adjustments:

Race: Venerable Magic-Blooded Half Elf Alignment: Chaotic Good
Flaws: Inattentive, Noncombatant
Traits: Polite, Honest

Level Class Feat(s)
1 Cleric(evangelist option) 1 Sacred Vow, Negotiator, Skill Focus: Diplomacy
2 Cleric 2
3 Cleric 3 Complimentary Insight
4 Warlock 1




Cohorts check:
7 ranks
7 Charisma
9 Synergy
2 Evangelist cleric
2 Mind domain
2 Herald domain
7 Motivate Charisma (+2 with eagles splendor on main char)
6 Beguiling influence
2 racial
2 negotiator
2 sacred vow
2 Mwk tool
3 skill focus

+53 total (+55 with ES on)

He casts Eagle's Splendor on the main character, and uses the Aid Another rules from Complete Adventurer to roll a Diplomacy check to modify his master's check. He'll get a 65 on average, or +6. He can get between +5 and +7.

Mathematical Breakdown of Diplomacy Check:

9 ranks unnamed
9 Charisma unnamed
9 Synergy synergy
3 Skill Focus unnamed
9 Motivate Charisma unnamed
2 Racial racial
2 Sacred Vow perfection
2 Evangelist cleric unnamed
2 Mwk tool circumstance
6 Beguiling Influence enhancement?
5 Friendly Face circumstance
4 Wednesday's Left Eye unnamed
9 Item Familiar unnamed
4 Herald Domain unnamed
2 Mind Domain unnamed
2 Negotiator unnamed
8 Custom item competance
1 Polite trait unnamed
1 Honest trait unnamed
5 to 7 Cohorts aid another check

1d20+94 to 1d20+96 Total

Summary:

At a mere 6th level, Fred has a minimum of +94 on his diplomacy check. He has soothing voice, so he can stop fights as soon as they start, and he has tons of class goodies. Even with a -20 circumstance penalty on his check, he still automatically converts a creature from hostile to friendly. 7 times per day, Fred can stop fights that have already started just by talking with his Soothing Voice ability (Will DC 104 average negates). And best of all, Fred isn't specific to any campaign setting.

Edit: Bumped it up to +94.