My choice is Edsger Dijkstra's mother, a lesser known, but, according to him, profoundly gifted mathematician, who, incidentally, inspired him to some heights of his own, better known, maths reasoning. Here she is in his papers: http://ewd.cs.utexas.edu.master.com/texis/master/search/mysi...

Unfortunately I couldn't find a decent Grace Hopper T-Shirt recently. There was the cobol.com t-shirt a couple of years ago, but it definitely should have used a more attractive picture...