owsley stanly was the the guy who made all the famous acid for the haight-ashbury crowd. he later became closely involved with the grateful dead - virtually their acid man. after his big bust (a BIG bust), he morphed into a guy called 'bear', and became the most famous of the dead's roadies. he's the guy who came up with the 'deady bears' and that famous logo of the skull with lightning bolts (seen from above).
but back when he was the king of righteous acid, he would make batches and sell/give away stuff to the good folks in the haight. for the monteray pop festival he did a famous run of stuff called "batman". he had a pill-tabber machine and he would put little logos on the pills. the batman acid was a purple pill with a batman logo on it. it was one of his most famous batches of great acid.
today, a tab of "purple batman" is like the holy grail of collectors of that stuff. i've only seen a sample of it once - an old friend had one in a bottle that he forgot he had in a drawer. it had been there thirty years (all the acid fadded out decades ago - acid has a short shelf life), and still looked new. it was pretty cool to actually see a little piece of history like that.