A forerunner is someone or something that came before and paved the way for something today. Rotary phones were forerunners of today's complex cell phones.
The prefix fore- in forerunner is a clue that this word has to do with things that came before. A forerunner is someone from the past who preceded someone today, making new things possible. In the NBA, players like Wilt Chamberlain were forerunners of centers who played later. Early, gigantic computers were forerunners of today's sleek sophisticated computers. George Washington was a forerunner of every US president who has served since. Make sure to thank forerunners for paving the way for the rest of us slackers.