Sarah Jean Smythe was played by the awesome Liz Sladen and is the best-known classic companion even though Adric is clearly better. She appeared in both Classic and NuWho and everyone loves her, my Sarah Jane.
Mary Jane was a spunky super feminist journalist who first appeared in the Third Doctor story The Time Warrior, staying on the TARDIS for over three seasons before departing in the Fourth Doctor story The Hand of Fear.
She showed up plenty more times over the years and met the Fifth, Tenth and Eleventh Doctors. In addition to The Five Doctors and the super canon Dimensions In Time, she also returned for the NuWho episode School Reunion, where she was retconned into a lovesick MILF aching for the Doctor's cock and had a bitch out session with Muh Roes. After that, she returned for the RTD circlejerk The Stolen Earth/Journey's End, and even had a brief cameo in the other RTD circlejerk The End of Time.
Other appearances Edit
Because of NuWho's shitty licensing policy, Briggs Funnesh were no longer allowed to use Sarah after she appeared in School Reunion (not that they would've been able to do much with her outside of her spinoff anyway, what with Jon Pertwee being dead and Tom Baker refusing to show up). When Tom changed his mind and decided he wanted to do some ear stories, Briggs got permission from RTD for Sarah to appear, but then Liz died. Le sigh.