As a professional, never look at someone else's salary and go "I deserve that".
Life is not 'fair', at least not in that way. There can be a million reasons why someone else makes more than you do. In the end it usually comes down to them having some form of extra value that you don't have, or them simply doing better during salary negotiations. Looking at what someone else makes and comparing yourself to them with your limited knowledge is a recipe for disappointment.
That doesn't mean that the information is useless. If you know that someone else in your role or a similar role receives a higher salary, this means that if you start salary negotiations, there's most likely room for your salary to grow. As usual in salary negotiations, don't make comparisons to others but speak to your own merits. Highlight the value you bring to the company. Explain why you're worth the extra money. Aim a bit higher than where you think you can realistically end up so that there's room for your employer to negotiate you down.
This last part is important: be realistic. No matter how underpaid you are, practically no employer is going to double what you earn. Excepting exceedingly rare cases, you'll have to change jobs for such a dramatic salary increase. To my knowledge, general wisdom is that you can generally negotiate a 10-20% raise without hard feelings. You can't realistically ask for more than a 20-25% increase without looking greedy.
In the case in the OP, this is slightly less relevant, but normally make sure you do your research of the market for your field beforehand, so that you know the general bounds of the salaries people in your role make. If a colleague in the same role makes dramatically more than the upper bound of the industry average that you find during your research, don't assume you'll be able to negotiate the same amount: it means they're probably adding some form of unique value that others in the role do not.
It's important to be realistic because if you ask for too much, you risk coming across as greedy which will make your negotiations that much harder. Only do this if you're willing to leave/get fired over the salary increase. If your manager feels like you put one over on him during the negotiations, this will cause you problems later.