“Knock. Knock”

“Who’s there?”

“It’s the 21st century and you still don’t have a doorbell?” This is “Better Know a Character.”

With the third season of NBC’s Emmy-hoarding show “30 Rock” premiering Thursday night at 8:30, I felt it was time to examine one of the unsung heroes of the show, Dr. Leo Spaceman (pronounced spa-CHE-mon, except by Tracy Jordan (Tracy Morgan) who pronounces it like it’s spelled).

Played by the crazy delicious “Saturday Night Live” alum Chris Parnell, Spaceman is the “fine doctor, and pretty good dentist” that gives his unique opinion to the cast of “TGS with Tracy Jordan.” His highly unorthodox medical advice is given some weight because Spaceman always has a confident and reassuring tone in voice.

With a medical degree from Ho Chi Minh City School of Medicine, Spaceman dabbles in all sorts of shady medical practices: offering pills to random people, completely ignoring patient-doctor confidentiality and endorsing any product regardless of its actual results.

Spaceman endorsed Tracy Jordan’s Meat Machine, which sandwiches meat between two other pieces of meat. “If it’s giving people meat, then I’m on board. I’ve always said humans need more animal blood. It keeps their spine straight.”

Aside from being listed under meth addiction and child psychology, Spaceman is in the Writers Guild of America health manual under fertility. When Liz Lemon (Tina Fey) has some questions for him, he prefaces the conversation by saying he cannot personally help her conceive. “Something happened to me while scuba diving.”

The fact that he cannot impregnate a woman did not stop him from writing a sex manual entitled “You’re Doing It Wrong.” Spaceman says it “guarantees male orgasm.”

Parnell’s performance of the misinformed doctor is flawless in every way. His subtle, Nick Riviera-like swagger makes his most absurd medical advice seem worth it as long as someone is videotaping the results.

Whether it’s stabbing dogs or calling 411 for “diabetes repair,” Spaceman is one of the most off-the-wall characters on “30 Rock” and the show is better for it. Here’s hoping he comes back for another season.

And don’t forget to watch the season premiere of “30 Rock” Thursday at 8:30 p.m. on NBC. If we don’t support this thing it could go the way of “Arrested Development,” and nobody wants that.