When: 1933 Why: First 127 film SLR. The first model was known as just "Exakta". This camera is also called Vest Pocket (VP) because of the 127 film, which was originally introduced by Kodak for its "Vest Pocket Kodak" camera. Some of the cameras were fitted with extremely fast f1.9 or f2 lens for those years, and they were called "Night Exakta".
When: 1936 Why: First production version of 35mm SLR, first system SLR, first interchangeable lens camera with bayonet lens mount
Ihagee was already known for the first 127 film SLR in 1933 and just in three years they introduced a first 35mm SLR too. But here is why I had to add "production" word: the first 35mm SLR prototype was a Soviet Union camera named Sport (Спорт) in 1934. Unfortunately it didn't go into production for another three years, so Ihagee stepped in first.