It is "L. Marcus" aka Lyndon H. LaRouche Jr. speaking on Columbia's South Lawn in the spring of 1968 during the Columbia Strike. He had been giving his Marxist Economics class at FUNY since the spring of 1966.
The strike committee organized workshops on the South Lawn near Butler Library before SDS got a hold of a frat house for the summer where the Summer Liberation School (SLS) was established.
We can see (literally) how the idea that "Len Marcus" really stood for "Lenin Marx" first arose.
He really believed he was the new Karl Marx!
Same question was asked in 1987.