Many of us know our great grandparents' names. One of my great grandmothers was a Vollick. I knew that, and I had proof (baptism, marriage, census records)
As I traced her lineage back, I found the trail stopped cold at *her* great grandfather, Isaac Vollick the Loyalist. I could not find him in New York before he arrived in the Niagara area of Ontario with Butler's Rangers. I hunted in every resource I knew of, to no avail. There simply were NO Vollicks running around south of the border in pre-Revolutionary times!
And then I stumbled on a very generous lady who steered me in the right direction with a casual remark "Oh did you know that your Loyalist ancestor Isaac Vollick used to be called Isaac Van Valkenburg?"
Huh? How the heck did one go from being a Van Valkenburg to a Vollick??!!! But she was absolutely correct in her statement. The reason I could not find any Vollicks running around south of the border was because it was not a "real" surname! My Loyalist ancestor simply adopted it. I think he adopted it as a nickname "Valk" (Dutch for falcon) from Van Valkenburg (meaning town of the falcon in Dutch) which may be what his comrades in arms called him. And it stuck. It became an established surname and there are thousands and thousands of Vollick descendants running around in America and Canada today.
There are also Follick descendants - because some of Isaac's sons and grandsons became known as Follick and that surname also stuck. I believe this alteration was due to the German/Dutch sounding "f" for "v". So instead of hearing Vollick, an English speaking/writing clerk no doubt heard Follick. And thus another surname was born!
That experience taught me to open my eyes to the possibility that a surname as we know may have changed greatly over the centuries. It may have been changed deliberately as in the case of my Isaac Vollick, or it may have been changed through mis-communication or mis-hearing.
For example my French LeRoy ancestor (prounced sort of like Le Wah in French - it's difficult to render it in text) settled in what is now Quebec in the mid 1600s. When he moved to New York, his name started being recorded as Larua, then Larraway. No doubt English speaking clerks mis-heard his name when he pronounced it! And so it began to be recorded as Larroway.
You must have an open mind when researching ancestors. You don't know if they changed their names. It may have changed due to mis-recording based on language differences. Did they change it to escape a bad situation? Did they change it simply due to having an established nickname that took hold? Whatever the reasons, if you are truly stuck on an ancestor, think about possible name changes. You may need to develop an entirely new area of thinking and researching!