Gol D. Roger is the rival and good friend of Luffy's grandfather, Monkey D. Garp. At the same time, Monkey D. Luffy inherits Gol D. Roger's will ( One Piece), Luffy is Roger's heir.
In addition, Roger's son Portcas D. Ace is the adopted grandson of Monkey D. Garp. Ace is Luffy's adopted brother. He is the son asked by Garp's old rival Roger to protect him. Garp originally wanted to train Ace to become a marine, but Ace became a pirate. When facing Ace's execution, he shed tears and lamented why Ace didn't listen to him.
Gol D. Roger has no direct relationship with Luffy's father, Monkey D. Dragon, and adoptive mother, Kali Dadan.
Extended information
1. Gol D. Roger
Captain of the Roger Pirates. The pirate group founded by Roger completed the voyage of the Grand Line and conquered the Grand Line, and was known as the "Pirate King" by the world. His words before his execution ushered in the "Great Pirate Era".
2. Monkey D. Garp
Vice Admiral of the Navy Headquarters, a legendary figure in the Navy, who once forced Roger, the Pirate King, into dire straits several times. Thirty-eight years ago He became a naval hero because he single-handedly blocked the attack of the Rocks Pirates in the Valley of Gods, protected the Celestial Dragons and the people, and teamed up with Roger to destroy the entire pirate group.
3. Luffy
Nicknamed "Straw Hat" Luffy, the captain of the Straw Hat Crew and the Straw Hat Fleet, one of the most evil generations. The Rubber Man, who has the power of the Rubber Fruit, has a bounty of 1.5 billion Berry. The dream is to find the legendary One Piece and become the Pirate King.