Strickland
From Tardis Wiki, the free Doctor Who reference
Assistant Commissioner Strickland was the senior police officer who visited Jackie Tyler after she informed the authorities of the Ninth Doctor's presence. In fact, Strickland was Sip Fel-Fotch Passameer-Day Slitheen, a disguised member of the Family Slitheen. The real Strickland had been murdered. Strickland revealed himself as a Slitheen and attacked Jackie and Mickey Smith in Mickey's flat. The Doctor, Rose Tyler and Harriet Jones assembled enough clues about the Slitheen's physical make-up for the Doctor to deduce their weakness. Jackie threw vinegar over Sip Fel Fotch, causing him to burst and coat them with the remains of his body. (DW: Aliens of London / World War Three)
