Did *Any* Companion of Paul Write Luke and Acts?

I am circling around the ultimate question of this thread, whether Luke, the companion of Paul, wrote the Gospel of Luke and the Book of Acts. A big reason this matters: if Paul’s companion, “the gentile physician,” wrote Acts, he had first-hand knowledge of Paul’s life and teachings. That would certainly increase the likelihood that he was giving an authoritative account!

The first step to answering the question — was it written by Luke? — was to show that Paul never *mentions* Luke as a...