Game concept
Legend Protagonist
The game also links it as Legend Protagonists.
From the game's encyclopedia
The Legend Protagonist is the main character of a Legend, whose the deeds are therein described. The owner of a Legend can also be its Legend Protagonist, but so can any member of their family — dead or alive, as long as they are 16 years old.
Legend Protagonists get no direct extra bonuses themselves, but the content about the Legend will be focused on them. They will, however, grant additional Legitimacy to the Legend Owner, based on how many Virtuous Traits they hold.
The Legend Protagonist must be an adult, for stating that an infant killed a dragon might be controversial.
The game's text for patch 1.20.1.2. Words in blue are entries of the encyclopedia: hover one to read it, as in the game.
Legend Protagonist is an entry of Crusader Kings III's in-game encyclopedia. The game explains it: "The Legend Protagonist is the main character of a Legend, whose the deeds are therein described." It is part of Legend. The game also links it as Legend Protagonists. Patch 1.20.1.2, from game/common/game_concepts/06_ce1_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/06_ce1_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.