Coach Wittenberg is voiced by James Belushi (better known as "Jim Belushi," brother of deceased Saturday Night Live cast member John Belushi. Jim Belushi actually was a cast member on SNL from the 1983-1984 season to the 1984-1985 seasonnote Jim Belushi lasted on SNL half as long as his brother, John, who was on the show from 1975 to 1979. He was the first SNL cast member to be fired, then rehired, and one of three cast members to have a brother who was also on SNL, joining Bill Murray [brother of Brian Doyle-Murray] and Dan Aykroyd [brother of Peter Aykroyd]. And, yes, that's the same guy from the sitcom, According to Jim).
One of Eugene's voices was both Numbah 1 and 2, as well as Sai. Eugene's original voice actor was Christopher Castile, who was on the ABC sitcom, Step By Step and was on an episode of Are You Afraid of the Dark? about a pair of stepbrothers who accidentally unleash the ghost of a convict while on a field trip to an abandoned penitentiary.
Arnold's Grandma Pookie is Charolette Pickles,Babs Bunny and Dot Warner (though the voice Tress MacNeille uses for the role sounds like Principal Skinner's mother [after the season one Simpsons episode where Bart goes to France and an Albanian boy comes to the Simpsons' house] and that crazy cat lady who first appeared on the season nine episode where Bart and Lisa are hired to anchor a kids' news show).
Christine Ebersole (of the 1981-1982 season of 'Saturday Night Live) voiced the short-lived boarder Lana Vail.
Name's the Same: There was a real politician named Pataki serving in New York while this show aired, specifically Governor George Pataki.
What Could Have Been: Helga was supposed to get her own spin-off set a few years into the future (around the time that Helga would be high school-aged), but the idea was axed because it would have been "too dark" for children's TV (in Nickelodeon's words, they said the spin-off would have been "...too much like Darianote though Daria never showed a miserable home life like the one the Patakis have. Yes, Helen and Jake sometimes put work before family and Jane and Trent are basically left to care for themselves because their mom is a hippie artist, they don't know who their biological father is, and the other siblings left for a better life, but it's not as painfully dysfunctional as Helga's family"). Considering the glimpses we got of Helga's miserable home life, rejecting the idea is either a wise decision to keep from traumatizing kids and incurring the wrath of Moral Guardians, or a foolish decision, as the Periphery Demographic of the show would miss out on an adult take on a kids' show that wasn't poorly-made, fan-written trash.
The 'Jungle Movie', which would have seen Arnold find his missing parents.
In the first season there was another tenant named Lana was originally going to have a crush on Arnold, getting him to do favors for her and regularly making him uncomfortable by sexually harassing him. Nick execs of course found this too disturbing and axed the idea. Since Bartlett couldn't figure out a new direction for the character, Lana vanished after the first season (save for some later cameos in flashbacks or the animators mistakenly placing her into scenes at the boarding house).
Word of Gay: Mr. Simmons. His voice actor is openly gay.
Word of God: All that's canon is that Helga confessed to Arnold in The Movie, and there are plans to go the Jungle to find his parents.
Helga's mom is an alcoholic and those "smoothies" she drinks are just a child-friendly substitute for booze as Nickelodeon is, first and foremost, a kids' network and, despite having adult jokes in it for the Periphery Demographic, references to alcohol and alcoholism is best left to the adult shows on Nick at Nite (though there are mixed alcoholic drinks that exist as smoothie-type drinks, like the daiquiri, the hurricane, and the pina colada).
Arnold's last name? Turns out it's been said many times by Phil: Shortman.
The show takes place in the Pacific Northwest, most likely in Washington State.