Dr. Samuel Register alias the Zookeeper, was a skilled geneticist in charge of the Upper Lamumba Research Center in Lamumba, Africa approximately thirteen years ago. He worked alongside the scientists Mark and Marie Logan studying the biology of the local wild life. One day, the Logans' six-year-old son, Garfield, encountered a rare green-capped monkey. The animal bit Garfield, infecting him with an extremely rare virus known as Sakutia. Mark Logan quickly culled together a serum that mutated the Sakutia virus, diminishing its lethal life cycle. However, Garfield still suffered from the contagion's side effects, which included green skin, and the ability to shape shift into different animals. Register was convinced that the Logans had inadvertently discovered the biogenetic missing link between animal and human.

Samuel became obsessed with their research, and pursued it long after the Logans' deaths. He later went on to secure a position at a government animal research center in Tampa, Florida. His tenure at the research center was rife with scandal with rumors circulating about the campus concerning his extreme and unorthodox practices. Unwilling to tolerate Register's eccentricities, the center terminated his employ. His work soon came to the attention of S.T.A.R. Labs, and they offered Register a position working at their San Francisco facility. S.T.A.R. placed him in charge of their abnormal and extraterrestrial disease program.

Register continued to experiment with biogenetics and accomplished many breakthroughs in his efforts to bridge the gap between animal and man. He eventually stole a sample of Sakutia virus from a CDC laboratory and began working on a process to create his very own animal army. During his procedures however, Register inadvertently infected himself with the Sakutia. He immediately began searching for a cure.

Shortly after infecting himself with Sakutia, Register discovered that the virus had mutated even further and had become airborne. Within a short span of time, every child under the age of thirteen within the San Francisco area found themselves suddenly shape shifting into a wide range of green-colored animals. As luck would have it, Garfield Logan, the only other person to survive Sakutia virus was presently active as a member of the Teen Titans known as Beast Boy. The airborne Sakutia virus altered Logan's biochemistry reversing all of its previous effects. He was no longer green, and could no longer transform into other animals. Logan eventually found Dr. Register and approached him for medical consultation.

By this point, the Sakutia side effects had begun to adversely alter Register's own genetic makeup. Rather than turning green like other victims, Dr. Register instead turned purple in hue. He believed that Logan held the cure to the virus inside his cell structure and rendered him unconscious with a tranquilizer dart. He prepared to cut Beast Boy open, when the Teen Titan known as Cyborg smashed his way into the laboratory, tackling Dr. Register. Register transformed into a giant serpent and carried his fight with Cyborg outside. Garfield knew that the only way to stop a changeling was with another changeling. He took a sample of Register's stolen Sakutia virus and re-infected himself, regaining all of his previous powers. Transforming into a giant green Tyrannosaurus Rex, he fought with Register on the streets of San Francisco. After getting in close, Beast Boy transformed into a Sydney Funnel Web spider and rendered Register unconscious with a poison bite.

The retroactive cure residing within Beast Boy's cell structure became airborne, curing Dr. Register and all of the affected children of the Sakutia side effects.


  • Metamorphosis: Samuel Register had the ability to alter his cellular structure in order to transform into any known species of animal. Through an act of will, he could shift from one animal form to another without returning to his original form first.


  • Genetics: Samuel Register was proficient in the field of biogenetics and the study of infectious diseases.
  • Toxicology
  • Dr. Samuel Register is rumored to be a hypochondriac, though he denies possessing such a condition.
  • Doctor Samuel Register may be named after Sam Register, the Vice President of Cartoon Network and a driving force behind the Teen Titans animated series.
  • In the Pre-Crisis continuity, Beast Boy was originally purple in color, not green. Dr. Register's skin turned purple, illustrating the fact that Sakutia could affect its victims in varying ways.



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