#1. Big Van Vader
The legendary Big Van Vader might have had only four successful title defences within the course of his three reigns as IWGP Heavyweight Champion, however, the late great Vader is arguably the most groundbreaking gaijin IWGP Heavyweight Champion in NJPW's history.
In 1989, Vader initially won the IWGP Heavyweight Title for the very first time in his career when he won an eight-man tournament by defeating Shinya Hashimoto to become the first ever gaijin competitor to win the IWGP Heavyweight Title.
After dropping the title to Salman Hashimikov, Vader eventually regained the title by dethroning his old-rival Riki Choshu to win the title. Through his stint as IWGP Heavyweight Champion, Vader held the title belt for a total of over 400+ days, with four successful title defences over the course of three different reigns.
Despite not being the strongest champion in terms of numbers, Vader's career in NJPW was certainly the turning point for every other gaijin competitor who had stepped foot in New Japan Pro Wrestling.