Does clone copying a legendary creature cause both to be put into the graveyard under the legend rule?

When Clone enters the battlefield as a copy of a legendary creature, it becomes a legendary creature with the exact same name as the original. You now control two legendary permanents with the same name, which triggers the Legend Rule (CR 704.5j).

State-based actions are checked immediately. Under CR 704.5j, if a player controls two or more legendary permanents with the same name, that player chooses one to keep and puts the rest into the graveyard. This is not a 'destroy' effect — it bypasses indestructible — and it is not a 'sacrifice' — it bypasses effects that prevent sacrificing.

Crucially, you choose which one survives. You can keep the Clone and put the original into the graveyard, or keep the original and put the Clone into the graveyard. You are not forced to lose both; you lose all but one (CR 704.5j).

Example: Your opponent controls Thalia, Guardian of Thraben. You play Clone, copying it. Both are now legendary and named 'Thalia, Guardian of Thraben.' State-based actions fire: you choose one to keep and the other goes to the graveyard. If you choose to keep the Clone, your opponent's Thalia hits the graveyard.

Note: if the Clone somehow ended up under a different controller than the original (unusual but possible), each player controls only one copy, and the Legend Rule would not apply — it checks per player (CR 704.5j).