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