Being a natural sperm donor?Watch
They tend to give the women aliases, online usernames or just a first name to avoid the possibility of ever being traced for child support payments.
Only guys that donate sperm for artificial insemination through a registered official agency have no parental or financially responsibility for any biological child born as a result of their agency donation.
Under those circumstances, the donors identity will remain anonymous until the child is 18 and then their name along with some contact information on file will be disclosed to those biological children that request it.
In Britain, guys that donate sperm without going through an agency or decide to enter into any direct agreement for 'natural insemination' with a random female stranger met online/friend/lover remain liable to pay child support.