Yesterday Harold is the past counterpart of Harold.
Yesterday Harold, along with Yesterday George were made when George and Harold, travelled back in time to take their test which they had failed, causing them to be separated. When the yesterday boys went to school, their older counterparts had ran out of food and money, and they went to the office to sell a comic. However, seeing two of the boys caused the teachers to think they were all dreaming and strip down to their underwear and getting arrested. Twelve days later, the Turbo Toilet 2000 attacked the city, and came for the Yesterday boys. When he attacked the treehouse, Crackers' eggs cracked and her children saved the boys. After putting Crackers and Sulu's children to bed, the Yesterday boys and their counterparts got prepared to face another sequel.