Is there a tool to visualize the academic citation network around a researcher?
You might want to have a look at the Web of Science (formerly known as ISI Web of Knowledge). When I started my PhD back in 2008, I used it particularly for visualizing citation networks relevant to my research. I think some time later it became a subscription based service, so the access is not as easy anymore, but a lot of scientific institutions or libraries may provide you the access. I haven't used the Web of Science any more in recent time, so I am not really aware of their capabilities today -- but the description still reads similar to what I remember.