Chummer is an anthropomorphic cat, and pickpocket that was first seen within Klugetown during Rarity and Applejack's search for Rockhoof's shovel.
Personality
Chummer is portrayed as slightly greedy, yet having a kind heart, and enjoys the life of a thief. He is also shown as more level-headed and smart, and not as easily swayed as Capper, him rather risking life as a thief than work under Verko, as he thinks it's all a scheme.
History
Chummer was once a tag-team thief alongside Capper, him stating that he would make up the plans, and Capper will make them work. When he and Capper arrived in Klugetown, Verko offered them both a place to stay, and a job working for him. While Capper agreed, Chummer refused to join him, believing it was all a trick. This lead to an argument between them both, and ultimately Chummer went his own way, leaving Klugetown and Capper behind.
Season 7
Chummer reappears within Klugetown again, attempting to pickpocket the locals when he was found by Applejack. At first he attempts to steal her Portal Key, which ends up failing, and him admitting that he was just trying to get by with all of his stealing. He tells Applejack about his old friend Capper, and believes that he was still working for Verko, much to his dismay.
Later on, he runs into Capper again shortly after Applejack and Rarity are captured, taking time to catch up with Capper and trying to get him to leave Verko behind by telling him his debt will never be paid. After being convinced, Capper joins Chummer in saving Applejack and Rarity, him specifically being the one to get rid of the guards and getting Applejack and Rarity free. By the end, he decides that he will stop pickpocketing, in favor for a new and better life with Capper elsewhere.