Who is the 'Companion' in ayat 50:23 and 50:27?

I'm working with the Abdullah Yusuf Ali translation. - [50:23](https://quran.com/50/23?translations=22) . And his Companion will say: "Here is (his Record) ready with me!" - [50:27](https://quran.com/50/23?translations=22) . His Companion will say: "Our Lord! I did not make him transgress, but he was (himself) far astray." - What is this Surah about in general?