A Serbo-Magyar coalition that invaded his territory was crushed at the Battle of the (*) Maritsa River.
This sultan executed his rebellious son Sawji Celebi, simultaneously forcing an allied ruler to pour vinegar in the eyes of his rebellious son Andronicus. This man made his close adviser Kara Halil Hayreddin Pasha the first kaziasker, a powerful judge administering military territories. This sultan's marriage to Czar Shishman's sister gave him hegemony over Bulgaria; he also made John V Palaeologus his vassal and captured Adrianople, which he made his capital. A Serbo-Magyar coalition that invaded his territory was crushed at the Battle of the (*) Maritsa River. Major innovations he pushed included the "blood tax," or devshirme, used to recruit Christians as Janissary soldiers that he then used in his conquest of the Balkans. Bayezid the Thunderbolt succeeded this ruler after he was stabbed by an enemy soldier pretending to surrender, Milos Obilic. For 10 points, name this Ottoman sultan who won, but was killed at, the 1389 Battle of Kosovo.
This sultan executed his rebellious son Sawji Celebi, simultaneously forcing an allied ruler to pour vinegar in the eyes of his rebellious son Andronicus.
Murad I [prompt on "Murad"]