I saw Glen Campbell in concert a total of three times. Amazing artist. To watch him perform Wichita Lineman in front of a full orchestra was a treat for the ears. He once said about that song in a performance-"This was considered a country song, but it has more chords than 5 country songs put together!"
He was part of the Wrecking Crew, (a group of studio musicians-who recorded music for famous artists) and was a member of the Beach Boys when when they were touring.
His voice in the above video isn't the greatest. I guess he had a performance- the night before this appearance-and was tired.
As an aside-a great Documentary to watch is "The Wrecking Crew" available on Prime, Hulu and other streaming services.