I wasn't able to find a list of all of the names Brandon has given Peter over the years, so I tried to make one myself. Did I miss anything?
There are no acknowledgements in any of his short stories, the Wheel of Time books, and the second Alcatraz book (At least, my copy). Peter is in the acknowledgements with no special name in Elantris, the first and third Alcatraz books, and The Well of Ascension. All others are in order, as best I could figure, of publication. They are capitalized or not as per the books.
He is the:
incalculable (Mistborn: The Final Empire)
Indivisible (The Hero of Ages)
insoluble (Warbreaker)
Inevitable (The Way of Kings)
Indefinable, Indispensable (Alcatraz Versus the Shattered Lens)
infused (Infinity Blade: Awakening)
Inseparable (The Alloy of Law)
incumbent (Legion)
interpolated (The Emperor's Soul)
intermittent (The Rithmatist)
infinite (Infinity Blade: Redemption)
incandescent (Steelheart)
incumbent (Words of Radiance--yes, I know it's a repeat.)
Inserted (Sixth of the Dusk)
Inscrutable (Legion: Skin Deep)
Insurmountable (Firefight)
Ineffable (Shadows For Silence/Perfect State)
Instant (Shadows of Self)
Immaculate (The Bands of Mourning)
incredulous (Mistborn: Secret History)
ininsouciant (Calamity)
Intrepid (Alcatraz 1 rerelease)
inconspicuous (Alcatraz 2 rerelease)
influential (Alcatraz 3 rerelease)
inaugural (Alcatraz 5)
Inciting (Arcanum Unbounded)
indisputable (Snapshot)
invokable (Dreamer)
Peter Ahlstrom.
Edit:
Here's the explanation Darnam mentioned, explaining how these began. http://brandonsanderson.com/annotation-mistborn-3-acknowledgments/
More names of the Peter: From the Coppermind: "There's "Ahstrom Square" in Luthadel, and a "Lord Peterus" in Alloy of Law. In Alcatraz, the green jacket Alcatraz wears is actually Peter's green jacket."
He is also Peet from the Bridge 4 crew, described as solid and reliable.
From Aether: