person providing identity for illegal operations
Solution 1:
I believe you are looking for straw man/person, straw owner or straw buyer. Straw itself is used also. When the context is bank fraud, I see the usage of middleman as well.
straw man: a person to whom title to property or a business interest is transferred for the sole purpose of concealing the true owner and/or the business machinations of the parties.
[legal-dictionary.thefreedictionary]
straw owner: ...is a person who owns property legally or has the legal appearance of owning something but does so on behalf of another, sometimes for a fee, and typically solely to hide the identity of the effective owner. Most instances of straw ownership are legal, but the arrangement is sometimes made for nefarious, illegal purposes.
[Wikipedia]
straw buyer: a person who makes a purchase on behalf of another person. A straw buyer is used when the real buyer cannot complete the transaction for some reason. It is not necessarily illegal to use a straw buyer, except where the transaction involves fraud or purchasing goods for someone who is legally barred from making the purchase themselves.
[investopedia]
Examples:
You must also be looking for evidence of payments by the principal to the nominee of services rendered. Note: The terms 'straw', 'straw owner' and 'straw man' are sometimes used to describe nominees and their transactions.
Money Laundering: A Guide for Criminal Investigators, Third Edition By John Madinger
Finding a straw owner comes next. It should be someone who needs money, won't ask too many questions, and isn't suspicious. Ideally it's a legal immigrant who doesn't speak fluent English and can be convinced what he's doing is legitimate. With a straw owner, the thief can then incorporate his new business with the state. He'll need to make sure his real name does not appear on the paperwork—only the straw owner's name.
How To Commit Medicare Fraud In Six Easy Steps / fastcompany.com
The bank claims fraud masterminds recruited people, mostly new immigrants, to be "straw buyers." For a payment of up to $8,000, these straw buyers would allow their name to be used to obtain the mortgage on the property.
'Straw buyer' seduced into mortgage scheme / cbc.ca
In another case, BAE secretly passed $10m via HSBC to a local middleman, Shailesh Vithlani, to obtain a radar contract. “It stank and was always obvious that this useless project was corrupt,” protested Claire Short, the UK’s development secretary at the time.
BAE moved money into Vithlani’s Panama entity, Envers Trading Corporation. As the cash flowed in, an HSBC manager met Vithlani in Dar es Salaam, Tanzania, and advised him how best to invest it. BAE was subsequently convicted of accounting offences in relation to the Vithlani transactions, and paid a £30m ($46m) penalty.
HSBC files: Swiss bank hid money for suspected criminals / theguardian.com
Solution 2:
You mean a person acting as front, or acting as an illegal front. You can also set up front companies or you can set up an illegal front company. In any case, "front" is an exact equivalent of "słup" in Polish when it comes to larger and international financial transactions.
Solution 3:
The person used to cash out laundered money may be called a (money) mule. They may be scanned into believing their work is legitimate. A similar but older usage is a drugs mule who is coerced and/or paid for transporting someone else's drugs.