Main story by Kirkman, Ottley & Crabtree
"The Secret Origin of Cecil Steman!" by Kirkman, Ottley, Rathburn & Shannon.
"Science Dog" by Kirkman, Walker & Plascencia.
*It's all been building to this. After five long years, the best superhero comic book in the universe has reached its monumental fiftieth issue! Invincible and Cecil Stedman face off and after this issue, nothing will ever be the same. Also in this issue, Science Dog returns in an all-new back-up story... and the origin of Cecil Stedman! *Source: imagecomics.com