|Theories may be removed if ...
Ben Plumm claims to have "a drop of dragon blood", as a member of House Plumm married a "dragon princess" long ago during the reign of King Aegon, although he does not know during the reign of which Aegon exactly.
Ben Plumm's claim of Targaryen ancestry could indicate his descent from Ossifer Plumm, who married Princess Elaena Targaryen in 176 AC, during the reign of King Aegon IV Targaryen. Ossifer died on the wedding night while consuming his marriage. Regardless, Elaena became pregnant and gave birth to a son, Viserys Plumm. Ben's descent from Viserys would fit with all of Ben's descriptions about his ancestry.
Tyrion Lannister later suggests that Ben instead had two drops of Targaryen blood, as it was rumored during the reign of Aegon IV and beyond that Ossifer had died before he could consume his marriage, and that Viserys Plumm had instead been conceived by King Aegon IV himself that night, following Ossifer's death. Viserys went on to have several sons, and Tyrion suspects that Ben descents from a younger one of these boys.
Readers have suggested another possible identity for Ben's Targaryen ancestry: Maynard Plumm, a hedge knight who lived during the reign of King Aerys I Targaryen and who claims distant relations to Viserys Plumm and who works for Ser Brynden Rivers, a bastard son of King Aegon IV Targaryen. Maynard is believed by many readers to in reality be Rivers himself, as his description by Ser Duncan the Tall matches the description of glamouring performed by Melisandre. An additional hint is given by an exchange Maynard has with Duncan, who comments on the rumours of Aegon IV's bastards by stating "We'd all be bastard sons of old King Aegon if half these tales were true.", to which Maynard replies "And whose to say we're not?". Lastly, as soon as Rivers himself appears, Maynard is nowhere to be found.
If Brynden Rivers, disguised as Maynard Plumm, sired any children, these children could have claimed the surname "Plumm".
The following arguments can be seen as counter-arguments for this theory:
- Any children Maynard would have fathered in his disguise would be considered bastards, and could therefore not have the surname "Plumm" unless Brynden got married as Maynard.
- So far, no one in the Seven Kingdoms seems to know that Maynard Plumm is Brynden in disguise. Even if Brynden, disguised as Maynard, fathered a child, there would be no one to suspect that the child had a Targaryen for a parent.