One of Nathan's campaign ads in the pilot states that he served tours in Bosnia, Serbia, and Rwanda, and he mentioned his days in the Naval Academy in passing to Claire. Adrian Pasdar played a Navy pilot in Top Gun.
In the episode Run!, Hope (insultingly) refers to Hiro as "Sulu." Hiro's father is played by George Takei, who played Sulu in Star Trek
In the episode An Invisible Thread, Claire mentions that she thought Nathan was right-handed after he signs a paper with his left hand. Nathan is actually Sylar in shapeshift mode and Zachary Quinto is left-handed.
Billing Displacement: Averted. Not only are the main cast members always billed in strictly alphabetical order, Heroes (along with Charmed and Eastwick) is one of the few non-soaps to credit just the actors who appear in each episode, instead of running a standard cast list.
Fandom Nod: Sylar explains that he, in fact, does NOT eat brains.
Also in one GN when meeting a trio of evolved humans who think of him as an inspiration, Sylar notes with some surprise "I have... fans!?" most likely a nod to the Sylar fandom.
Cast Incest: Heroes co-stars Hayden Panettiere (Claire Bennet) and Milo Ventimiglia (Peter Petrelli) dated while playing an onscreen uncle and niece.
Fake Brit: Adam may be British, but David Anders is American.
Fake Nationality: James Kyson is Korean-American, and doesn't speak any Japanese. He had to rely on Masi Oka and a dialect coach to help him speak the language correctly.
Samuel and Ricky are played by Americans Robert Knepper and Holt McCallany. Will and Caitlin are played by Brits Dominic Keating and Katie Carr.
While Mohinder is from India, Sendhil Ramamurthy was born in Chicago and grew up in Texas. Lampshaded by Ando who says (of white people, though): "They all look alike."
Franchise Killer: Season 4/Volume 5 ended up being the final season of Heroes, despite leaving a Cliff Hanger. Opinion is divided over whether or not it was due to Volume 5 itself, or just karma from arguably inferior previous seasons catching up. Actually, not only was the show cancelled, but they also ended up abruptly ending the graphic novels, and original plans for an end-of-series movie was also scrapped as well.
A particularly bizarre example occurred with Matt Lanter (Brody the rapist quarterback), who had previously been a regular on Commander In Chief, playing the President's teenage son. The weird part is that Hayden Panettiere had a guest role on Commander In Chief, and the two of them ended up making out. Hopefully, their prior... familiarity... made filming the rape scene a little easier.
Scully Box: Hayden Panettiere and Kristen Bell are very petite women, only coming up to 5'1" at best. They either needed the Scully boxes or wore heels in order to fit into scenes against Zachary Quinto (6'3) and Jack Coleman (6'2").
Star-Making Role: Hayden Panettiere wasn't exactly unknown before, but the show pretty much made her and Zachary Quinto much more known. It also hasn't done Masi Oka any harm.
Trope Namer: This series has named the following tropes:
The obvious example is how volume 3 was cut short, with plot threads obvious to be related to the main story ending up going nowhere. A bigger example would be the entire style of the series: The original intent was to have a revolving cast, with most characters not returning in future seasons. What could have been, indeed, if after season 2 we didn't have to deal with most of the extended Petrelli family?
The Aborted Arcs caused by the writer's strike, which led to the Seasonal Rot which the series never fully recovered from.
The Season 2 DVD had an Alternate Ending in which Peter failed to catch the virus vial that Adam had dropped. It was planned that the virus would have been unleashed, and the latter half of the season would have been dedicated to finding a cure with Maya performing a Heroic Sacrifice by using her plague power to absorb the virus, killing her in the process.
The writers were originally going to have a Kill 'em All ending at the end of season 1 and have a rotating cast each season. They didn't anticipate the characters becoming popular and developing a fanbase or Executive Meddling and it became increasingly difficult to properly use the Super Power Lottery winners like Peter and Hiro again.
Elle was supposed to show up in the "I Am Become Death" future as the mother of the little boy, but conflicts with Kristen Bell's filming schedule forced the writers to cut the Sylar/Elle arc short and kill her off.
She also was apparently going to be Claire's sister, but this was dropped (not necessarily a Petrelli though - the blonde hair indicates that they shared the same mother, Meredith, so they might have been half-siblings and Bob still her biological father).
Even after Season 2 was cut short and its original plot (the Shanti Virus) halted, Bob Bishop was going to play a larger role in Season 3, probably getting to use his power more and get some development (which, let's be honest, he desperately needed). Unfortunately, Stephen Tobolowsky had a terrible riding accident in the months leading up to production, one which nearly paralysed him and put his neck on the mend for months... so they Dropped a Bridge on Him with Sylar killing him offscreen for his ability, and he did little in his few scenes until this happened. To add insult to injury, Sylar never even used said power, and Bob's daughter Elle was killed off anticlimactically (as noted above).
Peter and Nathan were actually written to be twins, but since they had trouble casting the roles, they just aged up Nathan instead.
Sylar was not originally intended to be a watchmaker, but a middle-aged priest. The character was altered accordingly after the original pilot and after Zachary Quinto had read for the part.
An alternate version of the pilot showed that Ted Sprague's power originally belonged to another character named Amid Halebi. The character was going to be involved with a terrorist plot and had a history with Matt Parkman, but Tim Kring felt the storyline was far too controversial and cut it out of the final pilot. Halebi's ability was then reworked into Ted's story.
Tim Sale is the artist behind most of the art featured on the show, except for Sylar's art, which was done by Alex Maleev, Peter's first stick figure doodle (done by Jeph Loeb), and Molly's doodles, which the actress did herself. Sale and Jeph Loeb are frequent comics collaborators, which strengthened the show's ties to comics.
The vignettes that aired promoting new characters that would debut in the following season is a technique that originated in Professional Wrestling, specifically in Memphis, TN with The Fabulous Ones in the early 1980s and is still used today.