X was a mysterious and anonymous person who stole the Crystal of Knowledge from Tess Mercer, and then presumably mailed it to the Kent Farm as part of a scheme that sent Clark and Lois into the Phantom Zone.

Notes

• X's identity was never revealed on the show.
• Writer and producer Al Septien revealed that X was Lex in a twitter post: "As Lex ("X") recovered, his people stole it from Tess and he sent it to Clark hoping it would finish him by sending him to PZ." ^[1] However, it's unclear how Lex's team was able to reprogram the Crystal of Knowledge, a highly advanced piece of Kryptonian technology, to send someone into the Phantom Zone.

Quotes

X: (email to Tess): You are not ready yet - X.

Season Eight, Instinct

References