Question: What film producer co-created Mickey Mouse along with Ub Iwerks?

Context paragraphs:
Walt Disney: Walter Elias Disney ( ; December 5, 1901December 15, 1966) was an American entrepreneur, animator, voice actor and film producer.  A pioneer of the American animation industry, he introduced several developments in the production of cartoons.  As a film producer, Disney holds the record for most Academy Awards earned by an individual, having won 22 Oscars from 59 nominations.  He was presented with two Golden Globe Special Achievement Awards and an Emmy Award, among other honors.  Several of his films are included in the National Film Registry by the Library of Congress.

Minnie Mouse: Minnie Mouse is a funny animal cartoon character created by Ub Iwerks and Walt Disney.  She and Mickey Mouse were first drawn by Iwerks in 1928.  The comic strip story "The Gleam" (published January 19–May 2, 1942) by Merrill De Maris and Floyd Gottfredson first gave her full name as Minerva Mouse, although this is seldom used.

The Karnival Kid: The Karnival Kid is a 1929 American animated short film directed by Walt Disney and Ub Iwerks.  It was produced in black and white by The Walt Disney Studio and released to theaters by Celebrity Productions.  It is the ninth film in the "Mickey Mouse" film series, and the first in which Mickey speaks.  (During his first eight appearances Mickey whistled, laughed, cried and otherwise vocally expressed himself.)  Mickey's first spoken words were in this cartoon, "Hot Dogs!"  "Hot Dogs!" , the voice being provided by composer Carl Stalling.

Mickey's Choo-Choo: Mickey's Choo-Choo is a 1929 Mickey Mouse cartoon.  Ub Iwerks was the animator.  "Mickey's Choo-Choo" was released at the same time as "Springtime", the third "Silly Symphony" to appear.  It was one of the series of early Disney cartoons that led Mickey Mouse to become a national fad by the end of 1929. Originally in black and white, this cartoon was of the ten Mickey Mouse cartoons colorized by the Walt Disney Company in 1991.

SimEx-Iwerks: SimEx-Iwerks (formerly Iwerks Entertainment) is an American film studio founded in 1985 in Burbank, California, by Oscar winner and Disney Legend Don Iwerks and Stan Kinsey, two former Disney Executives.  The company was named to honor Don's father, Ub Iwerks, who was Walt Disney's first business partner and co-creator of Mickey Mouse.

Don Iwerks: Donald Warren Iwerks ( ; born July 24, 1929) is a former Disney executive, an Oscar winner, and co-founder of Iwerks Entertainment along with former Disney executive Stan Kinsey.  He is the son of the animator Ub Iwerks (Walt Disney's original business partner and co-creator of Mickey Mouse and Oswald the Lucky Rabbit) and father of Oscar nominated documentary film producer Leslie Iwerks.

Pete (Disney): Pete (also called Peg-Leg Pete, Pistol Pete and Black Pete, among other names) is an anthropomorphic cartoon character created in 1925 by Walt Disney and Ub Iwerks.  He is a character of The Walt Disney Company and often appears as a nemesis and the main antagonist in Mickey Mouse universe stories.  He was originally an anthropomorphic bear but with the advent of Mickey Mouse in 1928, he was defined as a cat.  Pete is the oldest continuing Disney character, having debuted three years before Mickey Mouse in the cartoon "Alice Solves the Puzzle" (1925).

Just Mickey: Just Mickey (alternately titled Fiddlin' Around) is a 1930 animated short film produced by Walt Disney Productions and released by Columbia Pictures.  The film shows Mickey Mouse playing a violin on stage as a one-person show; as indicated by the title, Mickey is the only character to appear in the film.  It was directed by Walt Disney and is the first Mickey cartoon not animated by Ub Iwerks.

Leslie Iwerks: Leslie Iwerks ( ) is an American producer, director, and writer.  She is daughter of Disney Legend Don Iwerks and granddaughter of Ub Iwerks, the animator and co-creator of Mickey Mouse and Oswald the Lucky Rabbit.  She has directed notable films including Academy Award-nominated "Recycled Life" and Emmy-nominated "The Pixar Story".  She has worked with non-profit organizations Save Our Seas, Safe Passage, NRDC, and Sierra Club to raise awareness on matters affecting the globe.  She currently helms Santa Monica-based production company Iwerks & Co.

Mickey Mouse: Mickey Mouse is a funny animal cartoon character and the official mascot of The Walt Disney Company.  He was created by Walt Disney and Ub Iwerks at the Walt Disney Studios in 1928.  An anthropomorphic mouse who typically wears red shorts, large yellow shoes, and white gloves, Mickey has become one of the world's most recognizable characters.

Supporting paragraphs: SimEx-Iwerks Walt Disney
Answer: Walt Disney