You may want to go to familysearch.org There you can enter the name of your great grandfather, include a range for his birth year 1830 1839 or whatever seems appropriate, enter a range of dates for his death, unless you know the exact year.
At least enter the country name. If you know the city, enter that too. Basically it's fill in the blanks with what you know, press enter, and see what they can show you that has to do with your ancestor.