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I.M. Pig is the head of the architectural firm Pig, Pig, and Pig. He engages in urban bird nest-building projects with his two associates, and considers himself to be "the greatest animal architect in the world."

In Sesame Street episode 3979, he approaches and solicits Big Bird with variously ambitious ideas for a new nest. He and his associates eventually present three models of potential structures, made respectively of straw, sticks, and bricks. Although initially miffed by the rejection of his proposals, he is eventually impressed by Big Bird's own nest-making skills and invites him to join his firm.

I.M. Pig's name is a parody of the real-life architect I.M. Pei.