Hi Kerry!
First of all, welcome to TCS!
It's a pleasure having you here and any advice is greatly appreciated from all of us.
We have 3 Persians and 1 Stray I took in last year. The ages go from 14 years, 9 years, and two 3-4 year olds respectfully. The 14 year old, Tedi, is also my cat. He has formed a special bond with my mom. He never really bonded with me or came to me for company. I try to spend some time with him, playing with him, feeding him, etc, but he loves my mom to death. Ever since I took the stray cat in, Lexi, who is a calico, he has constantly stalked her, picked on her, smacked her, and is just ruthless at times. All the other cats pick on her as well so my room is her sanctuary. The others are not as bad as Tedi.
What I can't figure out is that he never cared whether I spent time with another cat. Is he jealous? If so, why now? He spends more time in my room because she is in my room and I try to treat them both fairly, but he still goes to my mom as before. At times they can be nice to each other, but that is not often. It has been a year and I feel like the transition has not completed itself.
What is going on with him? I found out he has a heart murmur so I will also be taking him to a specialist to have it checked out. I am at a loss of what to do because I just don't understand his behavior.
First of all, welcome to TCS!
It's a pleasure having you here and any advice is greatly appreciated from all of us.We have 3 Persians and 1 Stray I took in last year. The ages go from 14 years, 9 years, and two 3-4 year olds respectfully. The 14 year old, Tedi, is also my cat. He has formed a special bond with my mom. He never really bonded with me or came to me for company. I try to spend some time with him, playing with him, feeding him, etc, but he loves my mom to death. Ever since I took the stray cat in, Lexi, who is a calico, he has constantly stalked her, picked on her, smacked her, and is just ruthless at times. All the other cats pick on her as well so my room is her sanctuary. The others are not as bad as Tedi.
What I can't figure out is that he never cared whether I spent time with another cat. Is he jealous? If so, why now? He spends more time in my room because she is in my room and I try to treat them both fairly, but he still goes to my mom as before. At times they can be nice to each other, but that is not often. It has been a year and I feel like the transition has not completed itself.
What is going on with him? I found out he has a heart murmur so I will also be taking him to a specialist to have it checked out. I am at a loss of what to do because I just don't understand his behavior.


I am so with you on that.

So to shead a little light on the subject, our cute little domestic kitties occupy A LOT of space on their own in the wild. For example a female can occupy 15 acres all by herself and males can occupy 150 acres all by themselves
....yes a 150 acres! So, when we put several kitties in one house, it can cause a world of trouble. Many times they duke it out over territory and resources, such as napping spots and food, even litterboxes. In a situation like this were the aggression has gone on for more than a year I recommend medication. We basically need to get Tedi to be less hostile/aggressive and Lexi to get some confidence. I would suggest approaching a vet in your area that has some experience with treating behavioral issues and advise them that you've spoke briefly with a cat behaviorist and that I think it is a good idea to try buspirone for Lexi to help build her confidence and Prozac for Tedi to make him less aggressive. This should help level the playing field in your home, because at this point, behavior modification will not do a whole lot since Lexi as learned to fear Tedi, her submissiveness eggs Tedi on and Tedi thrives on the thrill of chasing her, so it's a cycle that it feeding off of each of them, so medication I think would be the route to take. Also make sure there are plenty of resources and territory, such as plenty of food at several feeding stations placed randomly through out the home, and multiple litterbox stations also randomly placed through out the home, because Tedi cannot stand gaurd at all of them at once, so Lexi will always have a back up litterbox if needed. And also make sure there is plenty of 3-dimensional space, like window perches, scratching posts, and chairs for them to nap on, the more resources available, the less they will feel inclinded to fight over them. I hope this works for you, I wish you the best! 
Thanks! But my only question is that you recommend medication? Isn't there anything else they can try first? I just hate to see cats on meds if there are other solutions. 
I am taking Tedi in next week to have his heart checked so I will see what the vet says. Do you know why he is behaving this way? I have never seen him respond so aggressive ever in his life.