http://fireemblem.wikia.com/wiki/Gangrel

Originally a thief born in the slums, Gangrel was mistreated growing up, witnessing the robbery and death of his mother. Gangrel eventually rose to be the ruler of Plegia, and became known as the Mad King. Gangrel allied with the Grimleal and Plegia was turned into a religious dictatorship under the Grimleal. He enjoys war, and ignores Emmeryn's peace negotiations. Cruel and easily distracted, he enjoys deceiving others. After being recruited into Chrom's army, he begins to change his ways, partially due to a harsh past that weighs on his mind.

Gangrel spends much of the first half of the game trying to start a war between Plegia and Ylisse as well as acquire the Fire Emblem, with little success due to Emmeryn's pacifistic nature and the importance of the Fire Emblem to Ylisse. Gangrel's men kidnap Maribelle in order to further instigate a war and seize the Emblem, but the plan fails. After the attempted assassination of Emmeryn forces her to leave the capital, Gangrel attacks Ylisstol, causing Emmeryn to return to the capital to protect her people, allowing him to capture her upon her return.