Complex sentence: One of the oldest, and surely the most popular, is DIN 476, the standard that introduced the A4, etc. paper sizes in 1922, which was later adopted as international standard ISO 216 in 1975.
Split into simpler sentences: One of the earliest, and surely the most well-known, is DIN 476, the standard that introduced the A4, etc. paper sizes in 1922. This was later adopted as international standard ISO 216 in 1975.