The answer is: Luke

Acts 1:1 / Luke 1:3 - showing Acts to be a subsequent work of Luke.

The book of Acts is like the sequel to the Gospel of Luke, both penned by the skilled author whom we know as Luke, a physician by trade and a meticulous historian. This connection is quite intriguing; when you read through these books, you can't help but notice the seamless transition from the life, death, and resurrection of Jesus in Luke to the birth and growth of the early Church in Acts. It's almost as if Luke is saying, “Alright, here’s what happened next!”

Luke explicitly begins Acts by referencing his earlier gospel, which suggests both continuity and intention. He pours out his heart—detailing the actions and teachings of the apostles, highlighting the work of Paul, and recording how the Church spread from Jerusalem to the ends of the earth. The dedication of both writings to an unnamed “Theophilus” hints at a purpose, a desire to solidify the faith of this individual and, by extension, believers everywhere.

Interestingly, Acts offers trivia gold. For instance, many of the events includes not just the calling of the Gentiles but also addresses social justice, showing concern for marginalized communities. Moreover, Luke is unique among Gospel writers for focusing on women and social outcasts, giving his accounts an inclusive flavor. This sets up early Christian community dynamics that would ripple through the years, showing that growth wasn't just about numbers; it was about giving everyone a seat at the table.