Rugens was the Zeon officer in charge of the Zeon forces sent to Side 6 under the command of Colonel Killing to execute Operation Rubicon, a plan to steal the Earth Federation's newest Mobile Suit, the RX-78NT-1 Gundam Alex, which was secretly being developed there.
The initial phase of the plan involved the Cyclops Team attacking the EFF base where the Alex Gundam was being developed to either seize or destroy it. However, Killing secretly sabotaged the plan to ensure it would fail in order to gain authorization for his own plan, a nuclear bombardment of Side 6.
When the Cyclops Team failed though, Rugens ordered Killing to stand down and told him that using nuclear weapons would violate the Antarctic Treaty. Killing then told Rugens that Side 6 wasn't subject to the Antarctic Treaty and that he didn't take orders from him before shooting his superior and going ahead with the attack.
Principality of Zeon