I'll focus on the work-related issue.

Bill never wanted to do something he didn't come with. Got a solution about that problem that bugs everyone for 6 months, too bad, Bill doesn't like it, Bill doesn't do it.

As a consultant you're in a much better position to deal with this. If you ask Bill to do something, he's expected to do it unless he has a good reason not to.

His company is paying for your time and expertise, if Bill wilfully ignores your advice, then you document it, make the implications of failing to follow your advice clear, and ask whoever hired your company how they want you to deal with it.

In terms of 'Not wanting to work with him because he's a creep,' unless you believe you are personally at risk; I don't think it's a good reason, of course if you witness anything out of line you are morally obliged to report it. Unless you have hard evidence of his past misdemeanours, discussing them might open you up to being sued for defamation etc.

I am going to add an answer here, though it may be covered by some of the recent answers. But as you state you are a newly hired employee of consulting company, some of these answers that recommend "talking to manager", are not clear in talking to the client manager, or your consulting company manager.

As having 30+ years experience in the IT consulting world, you will find that you run into many of the same people in different companies and roles. Because you have had issues in past with a particular person, does not mean that you will in this engagement. People change. Perhaps they have been reprimanded or otherwise punished, and recognize their past bad behavior. Perhaps they are on probation, and working to overcome their shortcomings and issues. You would be prudent to give this person another chance.

However, you do have a duty to your consulting company and the client to bring up and confront any issues that will keep from successfully completing the engagement.

At this point, at the start of the engagement, I would have a talk with your consulting company account rep, or site manager, or whoever assisted in placing you at the client company. Let them know about your past history with Bill, and problems with Bill performing his work. Speak carefully but dispassionately of the sexual harassment issues, in that you are not repeating gossip. Only speak of your personal knowledge, or facts about his dismissal that you know. Ask your consulting company account rep/site manager what they want to do with this information, if they believe it should be brought up at the client company. Allow them to use their expertise, history, and relationship knowledge as to what the next steps will be.

In this way, you are shielding yourself with your new employer, giving them a heads-up about a potential problem. But you are not jeopardizing the consulting company - client relationship. You are also letting your new employer know that you have their interests in mind, not just your problems and issues.

You can't pick and chose who you work with, nor are you there to police peoples behaviour or provide "community service" by informing their employer of their past.

That last part might be confidential or private information btw.so bite your tongue!

If you have valid(!) professional reasons, inform your superior that those are why you can't work with the person.

If you have been harrassed by him, you can tell that your manager as well.

However, from what you said, I'm afraid you just need to be professional and suck it up.

You still can let your superior know that out of professional and private reasons you don't want to work with him.

If you're not the only one they can send and if your boss doesn't think you're being unprofessional you still might dodge that bullet.

Be prepared however that your managers opinion about you might shift negatively.

If you were personally harassed by Bill in a former job, and you have reasonable evidence of that fact, then you certainly have some grounds to tell your management why you don't want to work with him again. But your OP doesn't actually say that was what happened.

The fact that you think he will ignore your advice is irrelevant. Consultants are paid to give advice, not to enforce its use. (And considering the number of poor consultants around, it's just as well that some of them can't force their clients to follow their advice!)

If you can't handle the fact that clients often think consultants are nothing more than a time-wasting irrelevance imposed on them by their own managers who don't know any better, you are not going to have a happy working life as a consultant!

Managing Bill's behaviour is what Bill's manager is paid to do, and that is none of your business unless you are personally affected by it. Of course, if he does do something inappropriate, you know enough about his past not to ignore the first occurrence "in case it was just a one-off and you don't want to cause any trouble" - go straight to your manager (note, your manager, not his manager!) about it.

Talk it through with your manager, but treat it as your personal problem.

You do not have professional grounds to dismiss this job. As other answers well explain. Understand that you are the problem for business right now, so you'd better have a good reason.

IMHO, absolute professionalism is not the best way to go, and many people do understand you need to be able to look in the mirror after all. What is reasonable and where are the limits is a personal thing.

The best course of action is to do what's done with personal problems.

If your manager is reasonable, he'll convince you to take the job, or try to accommodate, and give you options, then it's your choice. From what you say, there is no guarantee you'll even have to work with Bill. Maybe they can swap you. Worst case it's do or die, but you won't know unless you find out. Trusting manager is your best option.

I think that personally talking to manager off-the-record is the best course of action because it let's you find out options without forcing anything yet - i.e. having least consequences, and you are not defaming anyone in any kind of (semi-)official setting. Then, you can prepare for official communication.

If the manager's not with you then there is not much unless you were personally involved, HR won't help you because there is no ground to protect your personal feelings before company.

^{(The following answer is edited out of comments I agree with, written by Fattie, PascLeRasc, and ESR)}

This is your boss's problem. Simply and clearly (without being dramatic) tell your boss about the sexual harassment background, and do that immediately without hesitation.

You should absolutely be honest with your boss about this. You have plenty of work-related evidence on the guy, both his insubordination and data theft, in addition to the sexual harassment. Your boss will likely be much happier to know these issues as early as possible and it'll build a good trust for your career.

The answer here is short and simple: "I am not comfortable working at Client X as they employ Bill who has a history of sexual harassment."