Captain Jack Harkness
In several instances in Torchwood, Jack displays no problems with killing a person of any species, which within Doctor Who, allows Jack's character to act in ways the lead character cannot. When reuniting with the Doctor in the 2007 series, he is verbally warned "don't you dare" when pointing a gun.  Witnessing the murder of his colleague Owen, Jack shoots his killer in the forehead, killing him in an act of quick revenge. Whilst the Doctor scorns Jack  for joining the Torchwood Institute (an organisation he perceives as xenophobic and aggressive), Jack maintains that he reformed the Institute in the Doctor's image; Jack himself had initially been critical of the moral failings of a 19th-century Torchwood.