English doesn't have a close equivalent to "Fulano".  However, you'll find that people will use such names as John Q. Public, Mr. Smith*, Mr. Jones*, Mr. Moviegoer, Mr. Shopper, Mr. Client, Mr. Customer, Mr. A., Mr. B., etc.  So-and-so is one of these names, but there is at least one problem: So-and-so is often used in English much like "filho da mãe" in Portuguese.  Be careful how you use it.  "John Doe" is commonly used when the name of a person is unknown or he represents a group of people (customers, clients, patients, etc.). 

*(Smith and Jones are considered very common names in English.  Surprisingly, they are Welsh surnames, not English.)

"John Doe" is historically the name given to an unidentified corpse.  If the corpse is that of a woman, then the name "Jane Doe" is used. 

If someone is arrested in the USA and he refuses to give his name, is unable to give his name (too drunk, too badly injured, no identification, etc.), in the arrest report he is identified as "John Doe" and so booked (registered, detained, and housed in a jail facility) under the name "John Doe".  In a large jail, you'll find several "John Does".  Often they are referred to as "John Doe 2", "John Doe 3", etc.  At the time of sentencing, if not before, an attempt will be made to learn the inmate's true name.