The Naguri Pirates were a group of pirates from Gol D. Roger's time.
The strength of the crew is generally unknown, though at one point they were powerful enough to be considered a challenger to the Roger Pirates. Naguri has Conqueror's Haki, lending to the supposed former strength of the crew as well.
At some unknown point in the past, the Naguri Pirates fought against the Roger Pirates, though they were easily defeated. Naguri offered his life for Roger to spare the crew, but Roger just walked away, leaving them all alive. Over time, the crew suffered major damage and eventually disbanded, with Naguri ending up in the Gray Terminal.
In Gray Terminal
Naguri was known as an old man who invented "weird stuff", according to Sabo. After saving Luffy, Ace, and Sabo from a large bear, he began to train them, and learned of Ace's father. In return, they helped him construct a new ship, and he eventually left the island to find his crew.