Christian Maclagan was a person who lived a long time ago and did some very important things. Like when you go to school and learn about different subjects, Christian Maclagan was interested in learning about something called "heraldry," which is all about symbols and designs that represent different things like countries or families.
Christian Maclagan wrote a really big book that had lots of pictures of different symbols and designs used in heraldry. People all over the world use this book as a reference to learn more about heraldry and the symbols that represent different things.
Since Christian Maclagan was so interested in heraldry, she also became the head of a very important organization that helps protect and preserve things like ancient buildings and artifacts that are important to history. She worked really hard to make sure that these things are taken care of and that people can learn from them even hundreds of years after they were made.
So, Christian Maclagan was a person who was really interested in learning about symbols and designs used in heraldry, and she worked really hard to share that knowledge with others. She also did important work in helping to protect and preserve history for future generations to learn from.