Doctor companion Sarah Jane Smith, played by Elisabeth Sladen who passed away on 19th April 2011. We shall miss her terribly!
An investigative journalist, Sarah Jane is a regular companion of the Third and Fourth incarnations of the Doctor, on the programme from 1973 to 1976 (seasons 11 – 14), and returns in the Fifth Doctor story "The Five Doctors" (1983), the 30th-anniversary story Dimensions In Time (1993), and most recently in the episodes "School Reunion" (2006), "The Stolen Earth"/"Journey's End" (2008) and "The End of Time" (2010) alongside the Tenth Doctor, played by David Tennant, and other companions of his era. She also appeared more recently with the Eleventh Doctor in Death of the Doctor, a story of The Sarah Jane Adventures. Source: Wikipedia, "Sarah Jane Smith", available under the CC-BY-SA License.