Magician

Magician is a Pokémon ability introduced in the sixth generation.

Effect
When a Pokémon with this ability hits another Pokémon with a move, it will steal that Pokémon's held item (if any) for itself. This ability does not work with Future Sight and Doom Desire.

It cannot steal from Pokémon that have Sticky Hold. Z-Crystals can't be stolen. A Griseous Orb can't be stolen if either Pokémon is Giratina, A Plate can't be stolen from a Pokémon with Multitype, a Memory can't be stolen from a Pokémon with RKS System, a Drive can't be stolen if either Pokémon is Genesect, a Mega Stone can't be stolen if either Pokémon is able to Mega Evolve using it, a Blue Orb can't be stolen if either Pokémon is Kyogre, and a Red Orb can't be stolen if either Pokémon is Groudon.

Trivia
Pickpocket is similar to this ability, except it only works with moves that make contact.