Protesilaüs was king of Phylace, in Thessaly, and a son of Iphiclus. He was the first one to leap ashore in the Greek expedition to Troy, in spite of the fact that the oracle had said that the first Greek to tread Trojan soil would also be the first to die.

His name thus comes from protos, 'first' and laos, 'army', or perhaps protos, 'first' and luo, 'to loose'. This could, of course, be regarded as merely a propitious or belligerent name, not a rash one.