Constant mocking from co-worker.

I could write a book if I were to tell my side of story from the beginning, so i'll keep it short and hoped I could get some advice on how deal with the problem I am having.

I work in an enforcement agency and I had this colleague whom constantly mocking me and asking people around me to stop talking to me. Whenever there's new people coming to our department he would tell that person about the mistakes I made before and I am not a reliable person to work with. Whenever I made mistake now and then he'll make a big fuss about it and ridicule me. If it were someone else he would just let it off and even help the person to resolve the issue.

He is a married guy with a daughter and his rank has been stagnant for the past 5-6 years and he had been in service for about 18 years while im just a female in service for less than 6 years. Both of us are same rank. He was my ex Team leader for about a years plus and I had many issues with him, I tend to question alot and showed my unhappiness if something I deemed unfair.

People around me had told me to ignore him which I did but that does not stop the constant verbal abuse from him even I am out from his team. He will insinuate me whenever possible and forming a gang to do so. He tried to pull people in but those people had told me they ignored him for his childish action. However, there's people who would make judgement based on what he said and that really upset me alot.

I admit that many times I did not put in effort to do work and made alot of mistake but I corrected my mistake. None of the mistake I've made has anything to do with him. I usually sit at my desk doing my own thing without bothering anyone but he would tease me when he walked past my desk.

I really wonder why he disliked me so much and I do not know what he was trying to achieve. Still, i am trying my best not to let him put me down but many times it hurts me alot and I tried to hide it. Any tips or advice to stay positive or even a counter-back would be good....