Arthur Horrocks is a wealthy, retired businessman who makes many contributions to charity. He took a liking to April after she ran an interview with him, and later invited her to his Hallowe'en party. After his prized golden Fabrege acorns were stolen, April summoned the Turtles to Horrocks' home in Rhode Island to investigate. Upon the finding and returning of the acorns, Horrocks revealed that some old plans to the house were now missing. Donatello surmised that they were stolen to reveal the location of secret passages throughout the house so that a band of kidnappers could make off with Horrocks and his rich party guests. After the Turtles met the Mutant Squirrel Super-spies, the two Mutant teams defeated the kidnappers and saved the day.
Mr. Horrocks is kindly and generous, using much of his wealth to make charitable contributions. Although taken aback when he first meets the Turtles (despite April having warned him that they were mutants), he takes their appearance in stride quickly, noting that he never judges someone by the color of his skin, "not even if it's green".
Horrocks has a habit of puffing on a massive Cuban cigar whenever he is working through a problem.