You know why "Game of Thrones" is so overwhelmingly popular? It's not because of the brutal violence and excessive nudity. Okay, it probably has something to do with that. But it's also because of the intricate and entertaining sub-plots that saturate the story. Sure, sitting atop the Iron Throne and raising baby dragons and whatnot takes up most of the screen time in "Thrones." But familial relationships, self-discovery and morality are all big themes jam packed into other engaging storylines that fans like to tune into.

Similarly, the NFL always has a multitude of sub-plots running at once. Each is as interesting as the next. So what are the three main storylines you should watch for in Week 9?

1. Tom Brady vs. Peyton Manning

The two marquee quarterbacks over the last decade-plus square off against one another for the 16th time this weekend. The Brady-Manning matchup is like Chris Farley vs. John Belushi; two respected titans going head-to-head for overall supremacy.

Brady is 10-5 in these games with 3,680 passing yards, 28 touchdowns and 13 interceptions. Manning has thrown for 4,371 yards, 31 touchdowns and 20 interceptions.

Brady has more Super Bowl rings, but Manning has all the passing records. Watching the two go toe-to-toe is a trick or treat for football fans. Rarely will you find a better matchup of quarterbacks. But with Brady turning 37 over the summer and Manning approaching his 39th birthday, we may not have too many of these epic duels left. Enjoy them while they last.

2. RGIII's Return

It's unofficially official that Robert Griffin III will start for the Washington Redskins this weekend against the Minnesota Vikings. Griffin has not appeared in a game since dislocating his ankle back in Week 2. The remaining eight games are critical for RGIII and the future of the Redskins.

Coming off a disappointing season last year, Washington hoped a coaching change and some added offensive firepower would get RGIII back on track to being the franchise savior he appeared to be during his scintillating rookie season. But Griffin's second major leg injury since being drafted has put those hopes in serious doubt.

Griffin's electric style of play and slight frame have made him susceptible to injuries, which have affected his play. The Redskins don't know if he can consistently stay healthy or become an effective pocket passer. While it's unlikely that Washington would move on from Griffin so quickly, this last half of the season is somewhat of a tryout for him. The Redskins (3-5) could be in the mix for a top five pick in next year's NFL draft. If Griffin fails to impress coaches over the next two months, the team could look at Oregon's Marcus Mariota or Florida State's Jameis Winston as potential replacements.

This Sunday will be RGIII's first opportunity to make sure that doesn't happen.

3. Andrew Luck's Season

Andrew Luck is currently averaging 342 passing yards per game, putting him on pace for 5,462. The NFL single-season record for passing yards, 5,477, was set last season by the man Luck replaced, Peyton Manning.

Luck came into the league as one of the most hyped prospects in recent memory. "Back in the summer of 2012, before Luck even played his first NFL game, one Colts executive mused that he thought Indianapolis' rookie quarterback already was one of the best five quarterbacks in the league," ESPN's Adam Schefter wrote.

No one can really replace one of the greatest quarterbacks of all time. But if Luck can break Manning's record just one year after he set it, then it will be another notch on Indianapolis' belt telling them they made the right decision. Keep checking in every week for Luck's chase of the record.