Genealogy of Influence is a dataset of influence links between historic figures started in 2005. I added the data to the database project Freebase where others have added thousands of connections. Some applications that use the dataset are listed below. The data can be accessed on Freebase here.
Changes to the Freebase API have broken these apps, sorry.
Genealogy of Influence is licensed under a Creative Commons
Attribution-NonCommercial-ShareAlike 2.5 License.
Wikipedia content is under the GFDL