He is shown to be a very old crab (over 100 years old since he's Krabs' grandfather and Mr. Krabs is over 70 years old) and wears tattered blue sailor clothes and light brown pants. He has an eyepatch over his right eye which has a large cut and has a large gray beard.
He has a black and white shirt and a black and gold belt. He has slightly darker red skin than Mr. Krabs, which is shown to be bruised, presumably due to fighting as a pirate.
Redbeard Krabs was born to a crab now known as Great Grandpa Krabs and an unknown Mrs. Krabs. He may have been born from one of at least two children, the other of which may have been Sally.
At some point, the two had a son, who they named, "Victor Krabs."
Sometime later, before Eugene Krabs, Redbeard's grandson, joined Grandpa Redbeard, he either divorced his wife or she died.
Sometime in or shortly after 1945, Redbeard took custody of the infant Eugene. Redbeard then taught Eugene how to be a pirate. Sometime after that, Betsy Krabs regained custody of Eugene and he lived out his childhood with her.
Several years later, Eugene had been a captain of his own pirate ship, but decided to fire his crew and sell the ship. That day, Redbeard had came to check up on him but did not learn that the ship was sold. He expressed pride that his only grandson had become a pirate though the latter tried to tell the truth but couldn't.