Bernard is the Knight Commander of the Lycian territory of Laus. He is the leader of Marquess Laus's army of Laus, the only person above him is Marquess Laus himself. Bauker served directly below him in the chain of command.
Bernard and the majority of Laus's army retreated during the attack on Castle Laus when commanded to do so by Darin, Marquess of Laus. The retreat was called for after the deployed Laus forces began losing to the group lead by Eliwood and Hector. The Laus army then invaded the poorly defended Lycian territory of Caelin, which due to the incident with Lundgren had a quite small force to defend it. The army from Laus then invaded Castle Caelin, forcing Lyn and her forces to escape while the Marquess of Caelin was captured inside the Castle.
In the previous Chapter 15 (16 in Hector Mode), Eliwood and Hector helped Lyn launch a counter attack on Castle Caelin, now occupied by the Laus forces. During that battle, Bauker who was leading the Laus forces outside the Castle was killed. The battle then continued inside Castle Caelin where Bernard lead a second force.
Bernard is a loyal man, and not particularly evil. His in game description reads: 'Knight Commander of Bern. Trusted by Marquess Laus.' This is, a translation mistake, as it is fixed in the Europe release. His decency is somewhat hinted at in his death quote, where he admits his death is a fair trade for Laus's brutality.