It's hard to compare NFL players across eras, and from different positions. It's hard to compare Dick Butkus' dominance at linebacker in the 1960s to Deion Sanders as a shutdown cornerback in the 1990s, for example.

But whatever the criteria, Aaron Donald is in the conversation for greatest defensive player ever.

The Los Angeles Rams defensive tackle retired Friday with a nearly immaculate résumé. He played 10 seasons and made 10 Pro Bowls. He was first-team All-Pro eight times, including his final season. He was a three-time NFL Defensive Player of the Year, tying a record. Some of the stats Donald put up were silly from a defensive tackle, though his legacy can't be told by just numbers.

Donald's career is over. He's a Pro Football Hall of Fame lock in five years. But the question upon Donald's retirement is bigger than just the Hall of Fame: Is he the greatest defensive player in NFL history?

Aaron Donald's GOAT argument

Donald was an intriguing prospect after a productive college career at Pitt, but dropped to the 13th overall pick of the 2014 NFL Draft because he didn't have prototype size for a defensive tackle at 6-foot-1, 280 pounds.

Then he changed the game.

All of the guards who signed $15 million to $20 million per year contracts over the past few offseasons should thank Donald. His dominance inside led to an even higher priority on interior pass rush, which caused teams to value guards higher. Not that any guard was stopping Donald.

The best way to sum up Donald's career isn't just the 111 sacks, awards or the Super Bowl ring he helped the Rams get. It might be the countless still shots of Donald being double- and triple-teamed by opponents, and still finding a way to beat them. According to NFL's Next Gen Stats, Donald was double-teamed on 40.5% of his pass rushes from 2018-23 and had 117 pressures against those double-teams, 33 more than any other player.

The term "unblockable" is used often but it has never been more apt than in Donald's case.

Donald had every team focusing all their efforts on stopping him and it didn't matter. In Super Bowl LVI, with the Cincinnati Bengals facing a make-or-break fourth down in the final minute, NFL Films recorded Donald's head coach, Sean McVay, saying "Aaron Donald's gonna make a play." And then Donald pressured Joe Burrow into unloading a pass for an incompletion to clinch a championship. That sums up Donald's career.

It's hard to make other NFL players look clearly inferior. Everyone in the NFL is a professional and among the elite of the elite. Donald made them all look silly for a decade.

Where does Donald rank?

It's hard to know where to cut off the list of contenders for the greatest defensive player ever. J.J. Watt, Lawrence Taylor and Donald, the three players to win NFL Defensive Player of the Year three times, are on the list. So are Bruce Smith and Reggie White, who have 200 and 198 sacks respectively. On the official sack list (it wasn't an official stat until 1982), nobody else has more than 160. Dominant players from other eras like Deacon Jones (he had 173.5 sacks, unofficially, via Pro Football Reference), Joe Greene and Butkus are worthy of consideration. Ray Lewis and Ronnie Lott are considered among the best ever at their respective positions and should be on the list too. Let's include Deion too because he's widely considered the greatest cover corner of all time.

How does Donald rank among them? His dominance puts him ahead of defensive backs Lott and Sanders. Greene was great for the Pittsburgh Steelers and changed the game, but Donald gets the edge among the legendary defensive tackles. As Donald does over Lewis, Butkus, Jones and Smith. Those players are all great, but Donald was better.

Donald gets the edge over Watt. The two were comparably dominant, but Donald's job doing it from the interior was tougher and injuries cost Watt a lot of time his final seven seasons (41 missed games). If you can pick only one player from the era, you'd likely pick Donald.

That gets us down to a group of three, the elite of the elite.

White vs. Donald is a great argument. White had 23.5 sacks in two USFL seasons; had he played those seasons in the NFL he'd be well above 200 and the all-time leader. White is one of the most dominant run defenders ever and happened to put up 12 double-digit sack seasons in the NFL. It's tough but White, barely, has the edge.

It doesn't matter because Taylor is better than them both. Taylor affected not just individual games but the entire league in a way that hadn't been seen from a defensive player before him, and hasn't been seen since. Donald isn't far behind Taylor, but he's still behind. So is White and everyone else.

So there it is. LT is the GOAT. White and Donald can argue over the title of greatest defensive lineman ever. Donald gets the title of greatest defensive tackle ever over Greene. And if you wanted to put Donald No. 1 overall, ahead of Taylor and everyone else, you have plenty of evidence to make a great case.

Donald was that good. No matter where he ranks in NFL history, there has never been anyone else like him.