He is shown to be a very old crab - over 100 years old since he is 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 (pink in "Senior Discount"), which is shown to be bruised.
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 could not.
Role in series
"Grandpappy the Pirate"
He is the main focus of the episode and comes to visit Mr. Krabs. Since Mr. Krabs started a restaurant and did not keep up his doings as a pirate, and lied about still being a pirate, he turned the Krusty Krab into a pirate ship. Mr. Krabs shows off the pirate ship, but eventually he ends up showing Redbeard that his pirate ship was actually just a restaurant. Despite this, Redbeard actually accepts the idea of a restaurant, saying that the prices for Krabby Patties are ludicrous.
In the end, Redbeard ends up stealing money from the Krusty Krab, making Mr. Krabs realize where he got his greedy ways.
"Lame and Fortune"
He appears at Dream Mr. Krabs' funeral.
He appears as a cameo in one of Mr. Krabs' paintings at his house.
He appears as one of the various relatives Mr. Krabs summons against Old Man Jenkins and his family.
His name is a reference to Blackbeard the Pirate.
Real pirates did, in fact, have rules, called the "Pirate Codex" or "the Code."
In "Grandpappy the Pirate," Grandpa Redbeard thinks that Pearl is a sea monster, which means that before that episode, he did not know or realize that she is his great-granddaughter.
Also, he is the first relative besides Mr. Krabs to appear in the same episode with her.
In "Senior Discount," he is pink rather than his usual red.
He has extreme longevity, since he is still alive considering that his grandson Mr. Krabs is over 70 years old and his son Victor is over 90, therefore, he has to be over 100 years old.
It appears this runs in the family, since Redbeard's father is alive as well and is way over 100 years old.