Janus

Janus is a mysterious individual opposing the Illuminati, appearing in the novel Deus Ex: Icarus Effect and Deus Ex: Human Revolution: The Missing Link, as well as the mobile spinoff Deus Ex: The Fall.

Background
Janus is a mysterious hacker, a member, and possibly the leader, of a cyber-terrorist group known as Juggernaut Collective, and is clearly opposing Illuminati in his actions, as evident from his involvement in Deus Ex: Icarus Effect, where he and his group aid Ben Saxon and Anna Kelso in combating the Tyrants, a group of black ops mercenaries working for the Illuminati.

He also makes an appearance in The Missing Link, where he contacts Garvin Quinn in the ending cutscene, who suggests recruiting Adam Jensen in their invisible war against the Illuminati. Janus dismisses the idea, stating that Jensen is too obsessed with finding Megan Reed at that point in time. However, Janus also states "(Adam) will find the truth in due time" and that they would find Adam if Quinn followed Janus' instructions exactly as specified.