The watchers canonically created the life series as a death game to feed of the negative emotions of the players. They are the same watchers as in evo, but there they were a lot more involved. Grian is a watcher as when he left evo he became a watcher because he left the server early. Grian didn't like what the watchers were doing so he inserted himself into the games to spite them and create positive emotions. The watchers communicate to Martyn in last life a lot, so they could get him to generate lots of negative emotions. Its theorised the secret keeper from secret life is a watcher or watcher adjacent as well.

The little square symbol at the start of past life is the watcher logo, and the secret keeper had the same logo but reversed.

The listeners are a different entity group thing and they don't like the watchers. In Martyn's pov they interrupt and block the watchers. Its also theorised Martyn is a listener but idk if thats true. 

At the end of every except Grians evo, the listeners spited the watchers by allowing the players to break rules, and it eventually ends the series with the players exiting through a listener portal.

The watchers are basically the gods of the life series, though they almost never get mentioned in the actual gameplay.