As the disciples stared into the sky after Jesus ascended, who suddenly stood beside them?

Answer: Two men dressed in white

Two men in white said, "This same Jesus... will come back in the same way you have seen Him go into heaven."

“They were looking intently into the sky as He was going, when suddenly two men dressed in white stood beside them. “Men of Galilee,” they said, “why do you stand here looking into the sky? This same Jesus, who has been taken from you into heaven, will come back in the same way you have seen Him go into heaven.””— Acts 1:10-11 (BSB)