John Loudon Macadam was a Scottish engineer and road builder who is best known for inventing a new method of road construction known as "macadamization." This involved laying roads with multiple layers of crushed stone of various sizes, which were then compacted and smoothed to create a durable and stable surface. Macadam's innovation greatly improved the quality of roads and became widely adopted in the 19th century. His work laid the foundation for modern road construction and maintenance techniques.