Already Paul says that Christ speaks in him. This is the underlying dynamic in the Gospel of Mark which is at once the Gospel of Jesus Christ. And so the "biographical approach" to the gospel is born. Mark "decided" to write a "life story" of Jesus. No he didn't. He used Jesus to talk about himself. But who was he? I strongly suspect he was Paul. In the Latin biographies of Paul it is clear that "Paulos" comes from a Hebrew title.