The ability to steal an opponent's creatures has been around since the inception of Magic: The Gathering. I have many frustrating memories of my step-brother dropping Control Magic or Binding Grasp on my Craw Wurms and the like in order to finish me off with my own creatures. I would finally manage to resolve a spell, only to have the creature stolen and used against me!
Wizards of the Coast has created numerous similar creature-stealing effects since the game's beginning. Clearly, it is intended to be a mainstay in Magic for the foreseeable future. Since Ice Age we've seen comparable effects in cards like Blatant Thievery, Dominate, Entrancing Melody, Invoke the Winds, Mind Control, and many more.
Note, however, that most of the time these effects are in Blue. Granted, Red typically has the ability so steal creatures as well, though only temporarily. Ever since Act of Treason was initially released in Core Set 2010, we've seen similar temporary effects time after time. In fact, many players have come to describe such cards as "Act of Treason" effects because they're so common.
There's plenty to choose from, but only if you're playing Red or Blue. What if you're sleeving up a Commander deck and don't have access to either of these colors? Are there other ways with which you can steal creatures from your opponents outside of Red and Blue, preferably permanently?
It turns out, there are!
Tertiary in Black
When Mark Rosewater describes abilities and the color pie, he shares how a given ability may be primary in one color, secondary in another color, and tertiary in a third color. I'm not sure what the official delineation is for stealing creatures (if one exists), but if I had to guess, I'd say that the ability is tertiary in Black.
Because of this, there are actually a few options you can access if playing this color. For example, the cleanest and most direct way of stealing an opponent's creature in Black is to cast Enslave.
I still remember reading this card when it was initially spoiled, and dropping my jaw seeing such a straightforward steal spell in Black. Granted, it's a far worse Control Magic because it costs two extra mana and pings you every turn. As far as stealing creatures in Black goes, however, this is a premium option. Luckily in games of Commander, taking one damage a turn is a minimal drawback.
If you don't want to go this route, and your deck includes many Vampires, you could choose an alternate route to steal creatures. Namely, there are cards like Captivating Vampire, New Blood, and Sorin, Vampire Lord that help you steal creatures permanently if you have Vampires in play.
I suppose if you'd rather play Rats instead of Vampires, there's also Piper of the Swarm.
As you can see, Black often requires some sort of sacrifice in order to permanently gain control of an opponent's creature. A lot of the time, the Black creatures are the cards that create this ability, though that's not always the case. Another example of the stealing effect on a creature is Infernal Denizen, an Ice Age creature that demands a sacrifice of two Swamps each upkeep to keep around.
New Blood is one non-creature spell that allows you to steal a creature. Another, much older example that I look back at fondly is Ritual of the Machine from Alliances.
With this one, you still need to sacrifice a creature, but it doesn't have to be a Vampire or Rat; any creature will do. The downside is you can't steal a Black or Artifact creature. Unless you're local metagame is filled with Mono-Black players, however, I suspect this card will still be effective and it's one your opponents will not expect.
Breaking the Color Pie: Green and White
If stealing creatures is primary in Blue, secondary in Red, and tertiary in Black, then my assumption is that Green and White have no business stealing creatures whatsoever. Unfortunately, despite Mark Rosewater's best efforts, there are still cards in these two colors that allow you to permanently steal an opponent's creature.
Let's start with White, and two strange Reserved List spells that allow you to permanently gain control of a creature. Not only are these effective ways of doing so, but they are also castable at instant speed, something that happens rarely in creature-stealing spells! Most of the time, stealing a creature requires you cast a sorcery, aura, or creature spell. Not when it comes to Jabari's Influence and Debt of Loyalty, however!
I think back in 1996 and 1997, Wizards of the Coast didn't scrutinize color pie breaks nearly as thoroughly as they do today. I assume that's how Jabari's Influence and Debt of Loyalty, from Mirage and Weatherlight respectively, were allowed to make print. As such, these are really powerful cards to include in your White Commander deck if you're looking to surprise an opponent by stealing their creature out of nowhere!
To add to the bizarre nature of these spells, these two White instants allow you to steal an opponent's creature permanently, with no easy interactive way to retrieve them. When Blue casts Mind Control on a creature, a player can destroy the Mind Control to get the creature back. With Debt of Loyalty and Jabari's Influence, the creature is stolen forever until it leaves the battlefield - either through dying or getting bounced.
The other White card I want to mention here is Preacher, which is a creature that allows you to steal an opponent's creature via activation.
Now we're getting Old School - Preacher dates back to 1994's The Dark. Unfortunately, with Preacher, the opponent gets to choose which creature you steal, so the card isn't nearly as powerful as the previous two White cards. Still, it's so rare to see a creature-stealing effect in White that I wanted to mention this one (also on the Reserved List). For those who appreciate funny Magic references, there's a sorcery from Time Spiral called Evangelize, which is effectively Preacher's activated ability on a spell with buyback. The fact that Evangelize steals creatures in the same way that Preacher does is likely not a coincidence.
Shifting gears to Green, there are very few options. In fact, in my research, I was able to identify one reliable way to steal a creature in Green: Willow Satyr, a creature from Legends.
The requirement that the creature you steal is legendary may seem prohibitive, but luckily in a game of Commander there are plenty of options. Shout out to the clause at the bottom of the rules text reminding you that you lose control of that legend[ary creature] when the game ends - important to know!
I have to imagine there are others, but I sure couldn't find any! It seems Green is the weakest color in this regard. As a result, a Green Commander deck will want to tap into artifacts that offer the same ability. I'd suggest Helm of Possession.
The artifact requires you sacrifice a creature in order to steal something, but it's a reasonable, colorless option if you're desperate for more cards with this effect.
Wrapping It Up
After finishing my research, I've concluded that every color has multiple powerful cards that let you steal opponents' creatures except for Green. It seems if you're mono-Green Commander deck is looking for play in this space, you're better off adding a second color. If that's not an option, then you're left with Willow Satyr and colorless effects like Helm of Possession.
That being said, there are plenty of options outside of Blue and Red to give you a surprising edge against an unsuspecting opponent. I wonder how many people in your play group have even heard of Debt of Loyalty and Jabari's Influence - both White instants can change the course of a game unsuspectingly with their powerful, permanent creature-stealing effects.
If you're not playing these cards, or some of the Black options such as Ritual of the Machine, I'd recommend trying them out. For now, these cards are relatively inexpensive despite being printed so many years ago. If they ever gain traction, they have the potential to climb in price. In the meantime, you have the opportunity now to test these cards out for a relatively small investment.