sperm donor

/S P ER1 M D OW0 N ER0/
noun
  1. 1

    A man who donates sperm, usually anonymously, to a sperm bank or fertility clinic.

  2. 2

    A man who is the father of a woman's child(ren), but no longer has a relationship (or has a hostile relationship) with the woman, and is typically uninvolved with the children as well. (Compare with baby mama).

Source: https://en.wiktionary.org/wiki/sperm%20donor