Game concept · All Under Heaven
Movement Leader
The game also links it as Movement Leaders, Movement Leader's, Movement Leaders', Leader.
From the game's encyclopedia
A character leading the Movement, delegated as the only member allowed to directly speak with Son of Heaven to further the Movements agenda using Make Movement Petition Decision.
To become a leader you either have to have the highest amount of Movement PowerMovement Power on previous leader's death or defeat the current leader in Debate Activity.
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.
Movement Leader is an entry of Crusader Kings III's in-game encyclopedia (All Under Heaven). The game explains it: "A character leading the Movement, delegated as the only member allowed to directly speak with Son of Heaven to further the Movements agenda using Make Movement Petition Decision." It is part of Movement. The game also links it as Movement Leaders, Movement Leader's, Movement Leaders' and Leader. Patch 1.20.1.2, from game/common/game_concepts/tgp_game_concepts.txt and game/localization/english/game_concepts_l_english.yml.
Source: game/common/game_concepts/tgp_game_concepts.txt, game/localization/english/game_concepts_l_english.yml and the English localisation, Crusader Kings III 1.20.1.2.