He is a large army green fish with brown hair and spiky teeth. He wears black pants and a dark blue jacket, and under it is a white shirt. His first name might be "Mac", as Patrick calls him this after sharing a cell together.
The Tattletale Strangler is notorious, as even the toughest fish are afraid of him. He is notable for strangling his victims after they rat him out, hence the name. He is first seen littering on the Krusty Krab property in his boat when SpongeBob is on litter patrol. After finding out that he is the one responsible for this, SpongeBob calls the police on the Strangler and succeeds in getting him arrested. However, due to his strength, he winds up escaping from his cuffs. Scared for his life, SpongeBob tries hiring numerous Bikini Bottomites to be his bodyguard, though everyone, even the toughest fish, refuses on grounds that they are far too afraid to deal with the Strangler.
He later encounters a man with a mustache reading a newspaper while waiting at the bus stop who offers to help him, who is actually the Tattletale Strangler under disguise to avoid being arrested again. Unaware of his true identity, SpongeBob hires him, much to the Strangler's excitement.
Afterwards, the Strangler suggests that they hide somewhere private so he can get revenge on SpongeBob for calling the police on him, unbeknownst to the latter. After several hours of running errands and attempting to gain entrance to SpongeBob's House, the two finally get inside and the Strangler is excited to get revenge on SpongeBob with no one around to see it. However, he is then interrupted by the two parties thrown for SpongeBob: his on-time party and his birthday party, much to the Strangler's irritation.
After the partying ends and the two are left alone, the Strangler finally plans to kill SpongeBob, only for Patrick to enter his house. The Strangler then lyingly suspects that he is actually the criminal, leading to the latter turning himself in. SpongeBob is left shocked, going on about how his best friend could do such things. Giving up, an infuriated Strangler removes his fake mustache and reveals his true identity and intentions. When SpongeBob asks how he did that without shaving cream, he tells him that it was a fake he bought at the party store, namely, the Phony Bolonga Mustache Emporium. Upon overhearing the word "party," the guests return to have the time of their lives.
The Strangler decides he can't take it anymore and attempts to leave Bikini Bottom. SpongeBob still believes he is his bodyguard and follows him for protection. Upon cutting off the strings of a parachute SpongeBob transformed into, the Strangler lands in the jail cell of the Bikini Bottom Police Department. There he meets SpongeBob and he is finally able to reveal he is the strangler through his poster which seems to surprise SpongeBob. The police congratulate him in putting the criminal behind bars, while the strangler is relieved to be "safe from that yellow idiot," only for his inmate to turn out to be someone just as annoying (or more so) as his former victim: SpongeBob's best friend, Patrick Star.
"What are you going to do, call the police?"
"Can we just go to your house?!"
"Open the door so I can strangle you! Uh, uh, I mean protect you."
"Forget the key! Let's climb through this window... I can't reach it. Do you think you can hop on my shoulders, kid?"
"Cleats? [SpongeBob falls on his eyes and he screams] Get your feet out of my eye sockets!"
"Close the door!"
"I've finally got you all alone!" [laughs evilly]
"He's not the Strangler! [rips off the fake mustache] I am!"
"Oh, it's a fake, you idiot! I bought it at the party store!"
"I can't take it!"
"Step on it! I'm being chased by a maniac!"
"Finally. Away from that guy."
"Look kid! I'm not your bodyguard! [cries] I'm the Strangler! [cries] See?!"
"At least I'm safe from that yellow idiot."
Oddly enough, when the Strangler takes off his fake mustache and thus reveals his identity, nobody recognizes him during the montage of him trying to leave Bikini Bottom.
Squidward also doesn't seem to recognize him when the third party is thrown even though he did earlier in the episode when telling SpongeBob who he is. They may been there to trick the Strangler into going crazy.
There are several implications that SpongeBob knew that his so-called bodyguard was the Strangler all along even before discovering his identity after he gets him behind bars:
Taking too long with his errands
Taking six hours and twenty minutes to get into his house, only to find out there was a key under his doormat the whole time.
Climbing on top of him to gain entrance by placing his spiky cleats in his eye sockets
At one point, he says "Don't mention it, Strangler—I mean bodyguard."
Sending everyone party invitations and throwing three parties in a row
Chasing him all the way to the police station and placing him behind bars