Father of a Thousand Bastards

A male character with a lot of children out of wedlock, almost always with multiple women. Alternately, the father is a sperm donor whose contributions have been used by many women.

This trope has nothing to do with Mother of a Thousand Young.

May result in The Seed is Strong.

Anime and Manga

 * Implied in Sister Princess, where the protagonist has an absent father and a dozen sisters who he'd never met before the start of the story.

Film

 * The concept of Delivery Man takes on this trope as it focus on David Wozniak, who donated his sperm two decades earlier, and now has up to 500 children as a result.

Literature

 * In the Ciaphas Cain book Traitor's Hand, Governor Tarkus' death causes a succession crisis, due to having no heir. However the crisis was made worse due to him preforming "almost two centuries of energetic fornication".
 * In the backstory of The Sword of Truth series, Darken Rahl sired numerous bastards but being a Complete Monster murdered most of them for not having inherited any magical talent. That's why he lacked a heir.

Tabletop Games
"Which reminds me of an idea discussed elsewhere: a party of PC adventurers who were ALL bastard offspring of Azoun IV. Ed did just this with a library PC group, although only the Cormaeril and the Thundersword sons knew their true parentage by the end of play. He’s not sure just how suspicious the other players were as to the bloodlines of their characters, but said the whole thing made for fascinating roleplaying [...]"
 * Forgotten Realms got the King of Cormyr, Azoun IV, who became rather infamous for this. Quoth his Royal Magician's comment (on seeing too many young nobles with familiar features at once) - "Moderation, my liege?" In Cormyr it's usually treated as a fact of life - "he’s just the most randy of a long line of lusty Obarskyrs; their ‘rutting reputation’ was part of the lore of the realm long before Azoun IV was born".
 * Also, developers on the game side played up his meme-worthy status and Champions of Valor got "Bastard of Azoun" as an optional regional background - in the list it's between "had music lessons as a kid" and "birth attended by a celestial creature (of any deity)".
 * The latter approach even had a precedent in Greenwood's own campaign:

Web Comics

 * Julio Scoundrél from Order of the Stick is heavily implied, if not out right stated to be this.

Western Animation

 * In Family Guy, due to the promiscuity of Glenn Quagmire, it is often joked about that he probably has many children he doesn't know about. One episode even has him run into a bunch of what appear to be his children all in different classrooms in the same school.

Real Life

 * Cecil Jacobson, a former fertility doctor in the United States, who during the 1980s used his own sperm to impregnate dozens of women while claiming it came from a mythical donor program.