Defender reduces incoming damage to its holder by 20 and discards itself at the end of the opponent's next turn. The Base Set wording reduced damage done to that Pokémon by attacks broadly, while the Undaunted wording specified the reduction applies to damage from an opponent's attack; a later errata with the Black and White expansion changed the wording from by an opponent's attack back to by attacks.
The card debuted in the WOTC era's Base Set with art by Keiji Kinebuchi and was reprinted in Base Set 2. It returned in the HeartGold and SoulSilver era's Undaunted with new art by Ryo Ueda. Our catalog lists 3 printings.
Defender's Japanese name is that of the X Defense item from the Pokémon games; the word Defender is also inscribed on the object depicted in the card's original artwork.
The Base Set printing is Defender's first release
The Base Set 2 printing is again credited to Keiji Kinebuchi
The Undaunted printing brought new artwork by Ryo Ueda
20 damage, after applying Weakness and Resistance.
The Black and White expansion changed the wording from by an opponent's attack back to by attacks.
From Base Set (1999) · 2 printings
Attach Defender to 1 of your Pokémon. At the end of your opponent's next turn, discard Defender. Damage done to that Pokémon by attacks is reduced by 20 (after applying Weakness and Resistance).
From Undaunted (2010) · 1 printing
Attach Defender to 1 of your Pokémon. Discard this card at the end of your opponent's next turn. Any damage done to the Pokémon Defender is attached to by an opponent's attack is reduced by 20 (after applying Weakness and Resistance).

Defender
Item
First printed in Base Set (1999)
Attach Defender to 1 of your Pokémon. Discard this card at the end of your opponent's next turn. Any damage done to the Pokémon Defender is attached to by an opponent's attack is reduced by 20 (after applying Weakness and Resistance).