The Sect Leader is the leader of a Sect.
Player Sect[]
See: Sect Leader effect on Branches
The Player Sect needs a Leader to be formed. It generally is the first Cultivator who is promoted, but this can be changed by the player afterwards. The Sect Leader is important in Branches, adding their Effectiveness score to every branch.
As such, it is often recommended to put a figurehead as Sect Leader with high Charisma and Social Skill Level at Primordial Spirit Cultivation Level, for example an 
Emotion Severing Law or a 
Shendao cultivator.
Other Sects[]
Other Sect Factions also have a Leader. These Sect Leaders and their preferences are randomly generated following the game's map seed.
Gifting liked items to Sect Leaders grants Favor and Connection. A given leader can only be gifted once for each item, but killing them outside their Sect map generates a new random Sect Leader, allowing the process to be repeated.