Short answers, pulled from the story.
Emperor Valens died on the field or perished in flames according to Ammianus Marcellinus Historiae book 31 chapter 13. His body was never found and his final fate remains unknown as he abandoned by guards during the rout.
Gothic forces were led by Alavivus and Fritigern who asked to settle in the Eastern Roman Empire after being displaced by Huns. Fritigern assembled forces at Nicopolis and Beroe to deal with the threat from Roman armies.
The battle occurred on the 9th of August 378 when Valens decamped from Adrianople leaving imperial treasury and administration under guard. He arrived at Gothic camp around noon after marching eight miles over difficult terrain.
Ammianus records Roman scouts estimated 10,000 Gothic troops but several modern historians estimate strength Gothic armies at 12,000 to 15,000 men. The entire force consisted of seven legions including Legio I Maximiana and imperial auxiliaries of 700 to 1000 men each.
Battle Adrianople signified barbarians fighting Romans or against them had become powerful adversaries despite losses not marking end Roman Empire because imperial military power only temporarily crippled. Defeat resulted destruction East Roman army core deaths valuable administrators destruction nearly all armories Danubian provinces following battle.