ted or theo are quite common abbreviations of theodore.
Theodore Marston went by Teddy.
Theodore Sorensen went by Ted.
Theodore Saidenberg went by Ted.
Theodore DeBonis went by Ted.
Theodore Bikel goes by Theo.
Theodore Sturgeon went by Ted.
Theodore McCoy goes by Ted.
Theodore Gershuny went by Ted.
Theodore Gearring goes by Theo.
Theodore Goodspeed goes by Ted.
Theodore Boborol goes by Ted, and Teddy.
Theodore Hesburgh goes by Father Ted.