Poor Oscar, no one remembers. 
from Wikipedia:
The patent for the Zerk fitting was granted to Oscar U. Zerk in January 1929, and the assignee was the Alemite Manufacturing Corporation (thus the eponymous names for the fittings). Alemite was already marketing ball check valves to accept grease supplied under pressure from a grease gun, such as for car and truck chassis lubrication points, both for OEM installations and for aftermarket upgrade kits which would screw in as replacements for stock grease cups. But Zerk's fitting was an improved style, less vulnerable to dirt and more forgiving of angled approach. Today many companies make these grease fittings.
from Wikipedia:
The patent for the Zerk fitting was granted to Oscar U. Zerk in January 1929, and the assignee was the Alemite Manufacturing Corporation (thus the eponymous names for the fittings). Alemite was already marketing ball check valves to accept grease supplied under pressure from a grease gun, such as for car and truck chassis lubrication points, both for OEM installations and for aftermarket upgrade kits which would screw in as replacements for stock grease cups. But Zerk's fitting was an improved style, less vulnerable to dirt and more forgiving of angled approach. Today many companies make these grease fittings.