Colonel Ackroyd was a soldier who teamed up with P.R.O.B.E. in 1995 to solve a series of killings involving the unexplainable disappearance of the victims' organs. He and Liz Shaw linked it to BEAGLE, believing that Julius Quilter had not killed the creature.
After Angela survived an attack and was subsequently killed in hospital, Ackroyd expressed frustration at Brian Rutherford's unwillingness to give him more men which would have allowed him to seal off the area and hunt down the creature. Ackroyd lost one of his men to the creature when they tracked it down to the moor, for which he was admonished by Patsy Haggard. He argued that he should have been properly briefed.
Ackroyd's men found and killed what they believed to be the creature in Quilter's house. However, Liz and Cummings determined that it was a fake and that Emerson was the creature. Ackroyd returned to the house and saved Liz and Rutherford by shooting him, which Liz also did with Emerson's gun.