what is this character's nature and personality?
lethally charming good looking and utterly captivating", as well as "flirtatious, cunning, clever and a bit of an action man". Jack's personality is relatively light-hearted
Jack Harkness
The character is described as both "lethally charming ... good looking and utterly captivating", as well as "flirtatious, cunning, clever and a bit of an action man". Within "Doctor Who", Jack's personality is relatively light-hearted, 
who does jack end up with in secret life UNANSWERABLE who is jack harkness? He is a fictional character  in "Doctor Who" and its spin-off series, "Torchwood".
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Jack Harkness [SEP] Development
The character is described as both "lethally charming ... good looking and utterly captivating", as well as "flirtatious, cunning, clever and a bit of an action man". Within "Doctor Who", Jack's personality is relatively light-hearted, although this changes in "Torchwood"'s first series, where he becomes a darker character. In "Torchwood"'s first series, Jack has been shaped by his ongoing search for the Doctor and also by his role as a leader, in which he is predominantly more aloof. In "Torchwood", he would occasionally inquire or muse about the afterlife and religion, sympathising with a man's desire to die. Returning in "Doctor Who" Series Three, Jack indicates he now maintains a less suicidal outlook than before.