It was Takemikazuchi no kami (who is variously called but we use this name after the shrine; also known as Kashima-sama), the enshrined deity of Kashima-jingu Shrine, who struck down the catfish with the spirit rock.
要石を打ち下ろし地震を鎮めたのは、鹿島神宮の祭神である武甕槌大神（表記は各種あるが鹿島神社に倣う、通称鹿島様）だといわれる。