Horst-Günther von Fassong (27 April 1919 – 1 January 1945) was a German Luftwaffe military aviator and fighter ace during World War II.

Flying with this wing, Fassong claimed his first aerial victory on 3 July 1941 during Operation Barbarossa, the German invasion of the Soviet Union.

Fassong was born on 27 April 1919 in Kassel, at the time in the Province of Hesse-Nassau, a Free State of Prussia within the Weimar Republic.

On 25 May, I. Gruppe was withdrawn from the Channel Front and moved to Krefeld Airfield for preparation for Operation Barbarossa, the German invasion of the Soviet Union.

Gruppe was moved to an airfield at Stara Bychow, approximately 50 kilometres (31 miles) south of Mogilev on the Dnieper on 12 July where it stayed until 20 August.

[10] Fassong was severely injured, sustaining heavy burns, on 28 July when his Messerschmitt Bf 109 F-2 (Werknummer 9650—factory number) burst into flames during takeoff.

Gruppe of JG 51, initially commanded by Hauptmann Hans Knauth and as of 1 March, by Major Rudolf Resch.

In that combat area, Army Group Centre had launched Operation Büffel, a series of retreats eliminating the Rzhev salient.

[13] On 10 June, during a Soviet attack on the Seshchinskaya and Bryansk Air Field, Fassong claimed three aerial victories in nine minutes.

Gruppe was ordered to an airfield named Oryol-West and supported Generaloberst Walter Model's 9th Army on the northern pincer.

[15] The Gruppe claimed 36 aerial victories that day, including two Lavochkin La-5, an Ilyushin Il-2 ground attack aircraft, and a Douglas A-20 Havoc bomber also known as a Boston, by Fassong.

[18] On 14 August, Fassong again became an "ace-in-a-day", and was credited with five Il-2 ground attack aircraft shot down west of Kharkov during the Soviet Belgorod–Kharkov offensive operation.

[20] On 8 May, the United States Army Air Forces (USAAF) attacked Berlin and Braunschweig with 807 four-engined heavy bombers escorted by 855 fighter aircraft.

[21] JG 11 intercepted the bombers of the 1st and 3rd Bombardment Division on its way to Berlin in the vicinity of Verden an der Aller.

[23] In total 886 four-engined bombers, escorted by 980 fighter aircraft, headed for the five main synthetic fuel factories in middle Germany in area of Leuna, Merseburg, Böhlen and Zeitz, and the Protectorate of Bohemia and Moravia and Brüx.

[28] In late May, Fassong succeeded Major Anton Hackl as Gruppenkommandeur (group commander) of III.

[42] At 06:30 on 1 January, Fassong briefed his pilots of the operation and that their target would be the Asch Airfield (Designated: Y-29) located north-west of Maastricht.

[30] According to Spick, Fassong was credited with 136 aerial victories, 90 of which claimed over the Eastern Front and 46 in the western theater of operations, including four heavy bombers.

[47] Obermaier lists him with 75, potentially about 80, aerial victories, among them 10 claimed over the Western Front, including four heavy bombers.

This figure includes 61 aerial victories on the Eastern Front and two heavy bombers over the Western Allies.