A messenger sent before to give notice of the approach of others; a harbinger; a sign foreshowing something; a prognostic; as, the forerunner of a fever
{i} ancestor; one sent in advance, one who comes before; sign of that which is to come, portent, omen
anything that precedes something similar in time; "phrenology was an antecedent of modern neuroscience"
If you describe a person or thing as the forerunner of someone or something similar, you mean they existed before them and either influenced their development or were a sign of what was going to happen. a machine which, in some respects, was the forerunner of the modern helicopter = precursor