Aggressive Cat Behavior

Question
In the past few months my cat has become surprisingly aggressive towards my father.  During a normal episode of such aggression, my cat, Lucy, will bristle, with a bushy tail, and hiss.  In few extreme cases she has actually lunged or attempted to claw him.  These episodes usually occur near the stairs, with her at one end and him at the other.  She has only displayed violent behavior towards my father, and this started quite suddenly a few months ago.  She is ten years old.  Do you have any ideas about the cause for this aggression, or possible solutions?

Answer
Hi Evangeline!  I can see where this could be a problem.  Has your father accidently stepped on her tail or foot?  Sometimes, if this happens, a cat will associate the person who accidently stepped on them (ect.) with pain and will react in this way.  
Have your father give Lucy treats by setting them down in front of him.  Every time a treat is given, it should get closer to your father until she will take it out of his hand.
Is your cat feeling well?  Sometimes, if ill, they will act out in aggression.
How has your father and Lucy's relationship been throughout the years?  If your father has been unable to pay as much attention to her as others in your household, maybe him spending one on one time with her will help her get comfortable with him once again.
This is odd behavior as cats do not normally turn on someone like this, and to be honest, this has me quite baffled as to why she is behaving like this.  I feel bad for your dad!  I would recommend a vet visit to ensure that her health is well and this is not a behavior due to an illness.  If this problem persists or becomes any worse, your veterinarian can also prescribe a very low dose sedative to keep her calm.  I am going to do some research on this and talk to some of the veterinarians I work with to see if there are any other suggestions of cause and treatment out there.  I will definately get back to you within a few days to let you know what I have found.
Hang in there!
Hilary