At the time the diary was written, M.G. Brubaker was a Mennonite school teacher in East Petersburg, Lancaster County, Pennsylvania. He married Mary D. Stuben in 1902. He was the son of David N. Brubaker and Lizzie Gottschall and grandson of David Brubaker.
More detailed information about his education and career can be found in the back of the diary. Further information about this individual or organization may be available in the Special Collections Research Center Wiki: http://scrc.swem.wm.edu/wiki/index.php/M. G. Brubaker.