Long johns are a type of thermal underwear designed to provide warmth in cold weather. They typically consist of a long-sleeved top and long pants, made from materials like cotton, wool, or synthetic fabrics. Long johns are often worn as a base layer under regular clothing, making them popular for outdoor activities in winter. Originally developed in the 19th century, long johns were named after the famous circus performer John L. Sullivan. They have remained a staple in winter wardrobes, especially for those who work or spend time outdoors, as they help retain body heat and keep the wearer comfortable.