We do not have "Kaiser" (meaning "emperor") as a first name here in Germany, only as a last name. The German version of "Caesar" would be "Cäsar" and it is pronounced like "TSAY-zar".
Kaiser is not the German form of the name Caesar, it is the German word for "emperor". It is not used as a first name in Germany, only as a surname. [noted -ed]
The confusion for this name comes from the fact that the German word for Emperor, "Kaiser," is literally the Germanic spelling for the "Caesar," which in Latin had a hard 'C' sound, and an 'AY' sound for dipthong AE (Æ).
And yes, no one in Germany is named this. It would be similar to naming your son "emperor" in an English-speaking country.
Keyser Söze (pronounced Like 'Kaiser') is a fictional character in the 1995 movie 'The Usual Suspects'. In 2003 the American Film Institute named him the 48th greatest movie villain.