As far as personal characteristics that are more attractive, many were already described here. I don't think it is only one characteristic, rather a combination. Generally speaking, I believe that being more laid back, cool, relaxed, non-chasing, non-judging and genuine are good things to work on. Abundance mentality is good. No neediness, no clinginess, more independence... Ability to make decisions, ability to go for things that you want... Find some passion in life, go for it... Being positive is good, you don't have to be a clown but having optimistic views in a sense "can do what I focus on" is pretty good. Some seriousness, e.g. you work hard at school or at work, or on your business is good, it also gives you a good edge...
But again, what does it mean "strong leader"? Do you believe that people want to be lead, and if so, in which situations?
... It all depends on personality and what you want. For example, you work at low paying job, the education is not so high, the overall motivation of workers is low, there is not much responsibility. For them it is just a job they don't care about, just put in couple hours per day, collect paycheck and go home. So strong leader in this group (boss, Alpha or whatever you want to call it) have to be more strict, more pushy around, giving specific tasks, perhaps rewarding extra effort and so on. He needs to persistently motivate them to keep or increase performance. This kind of leader should probably have higher education than average workers there. If he is more laid back, if he doesn't care much, well the company may not survive...
Take another group to compare, say you work at high paying jobs and work around highly motivated, ambitious and competitive people. It is a totally different approach, if you push them around like the above group they will mostly dislike you. You don't have to tell them what to do, you don't have to give them extra tasks to 'survive' the day at work. They also want to collect paycheck, so maybe you have to find way how to motivate them differently. The leadership may be more of finding out what they want and like, and enabling or allowing them to go for it...
The same with other groups, some groups simply don't want the classical "Alpha" leader, yet the others may desire it... For example, I had a group of friends. We were just guys, there was no "leadership" in group, no "Alpha", all was good. Then I decided to go for higher education, to move my life forward. The guys I knew were like my brothers since I was little, but most of them don't talk to me now. I sort of expelled myself from that group by trying to be "better". I became better in a sense of education, but at the same time I no longer "fit" in that group, just because of that...See, when people perceive you as "too good" they may not like being around you, because they feel inferior... If you feel inferior around somebody, you simply don't want to be around...
Exactly the same with girls, if you are "too good" (in other words, constantly self-improving masturbator) she may like you a lot as a guy but she may easily fall in auto-rejection. Why is that if you are such a good guy and does all things the right way? Well, that is the exact reason, she knows she doesn't do things the right way, she knows that she can't offer you the same things as you are expecting from yourself... She feels inferior, thus she goes to auto-rejection. Quick example: you are a muscle guy, all toned, all healthy food, and she is just cute/silly/pretty girl who doesn't care much about fitness. Do you think she wants to be seen around you on a beach? Some may, others won't...
... I believe Trump is a master in business, he is a brilliant guy, he is a "strong leader". If he only polishes his speeches little bit, if he only were more careful with how he says things, he would be much more popular. He sees things from both sides (Democrats, Republicans) vs e.g. Obama who is only one-sided. He is able to select what is good in each group and emphasize it in clear way. At the same time he emphasizes the negative things and connect them to the other candidates. He is also tough, he make people do things his way, the way he wants it... He may be a great boss, many businessmen may love him as a leader, they would do everything to work for him so they can learn - but would they want to be around him for dinners and fun time? Have a beer and spent free time? Probably not, he doesn't "fit" into their close friends group...
So there is difference between being "strong leader" and being "fit" for that particular group...