Liberius Mikulitsyn Timeline and Summary

Liberius first shows up after his boys have kidnapped Doctor Zhivago and forced him to be a military doctor for their left-wing militia, which is known as the Forest Brotherhood.
Liberius is convinced that his Communist ideas are right, and that Zhivago is wrong for being a stubborn, selfish, individualist. He invites Zhivago into his tent constantly to have long discussions about military tactics and philosophy.
While he's at it, Liberius also becomes addicted to the cocaine that is supposed to be used as a painkiller for wounded soldiers.
As his army marches on to victory, Liberius also takes every opportunity he can to execute his political rivals. His passion for Communism and the good of all humanity is kind of undermined by his passion for killing people to get what he wants. But, as Pasternak points out, that's actually pretty common with Communism.