-ko is a Germanic and Old High German diminutive suffix used to create diminutive forms of names. A variant form is -ka.
Originally the ending was used for both genders. Today it is only used for male names.
In Old High German it changed to -cha which later merged with another Germanic diminutive -īn (see also -chen).
In Frisian and Low German it changed to -ke, sometimes shortened to -k.
A creative spelling variant is -co.
List of Names with the suffix -ko