Wilhelm Casper is a secondary antagonist of Full Metal Panic in the Light Novels, as well as possibly a antagonist of the 4th season of the anime Full Metal Panic: Invisible Victory.
Of German nationality, Casper yielded a reputation of having the furthest practical sniping distance, and was a mentor of Kurz Weber, teaching him the ways of sniping for a long time. Actually, Weber didn't have a good relationship with his teacher: Casper was known for never missing the shot, no matter what or how many people were in the way, it was a policy that sickened Weber and eventually he ended up ranking up as Sgt. in Mithril.
At some point, Casper reached contact with Amalgam and became a member of it.
Casper was newly introduced, Now wielding a Plan-1065 Erigor, shortly after Leonard destroyed Sousuke's Arbalest, and he began to use the ARX-8 Laeviatan. Mithril's response team are sent into the Soviet Union, to Yamsk-11, eventually Amalgam's enforcers reach the Yamsk-11 as well, and Casper entered a sniping duel with his former pupil, Kurz. The duel ends when Casper shots Weber and fatally wounds him, leaving him to die without any remorse. Casper then leads the Amalgam's taskforce and captures Melissa Mao and few other Mithril's operatives, using them as hostages, He warns Sousuke he must surrender, as they are heavily outmached. But Weber, being still alive, communicates to Sousuke via their radios that he must lure Casper to his position, and to get a clear shot he needs him out of his arm slave. Sousuke taunts him, Casper leaves his Erigor, and finally Weber mortally shots him, realizing he has lost his precious title of most effective sniper, before passing out.
- It is said that he will be a secondary antagonist in the new season of the anime of Full Metal Panic, although this is unconfirmed.
- A team formed by Leonard Testarossa was formed in the late light novel's parts, in order to act as a response against Mithril's taskforce members, with Wilhelm Casper acting as the counterpart of Kurz Weber.