Conversation so far:
What did Jared Leto perform?
Jared Leto is the lead vocalist, multi-instrumentalist and main songwriter for Thirty Seconds to Mars.
What was Jared Leto's band name?
Jared Leto formed the rock band Thirty Seconds to Mars  with his brother Shannon.
What year was Jared Leto's band, Thirty Seconds to Mars formed?
Jared Leto formed the rock band Thirty Seconds to Mars in 1998.
Where was Jared Leto's band, Thirty Seconds to Mars formed?
Jared Leto formed the rock band Thirty Seconds to Mars in 1998 in Los Angeles, California.
What state was Jared Leto's band, Thirty Seconds to Mars formed?
Jared Leto formed the rock band Thirty Seconds to Mars in 1998 in Los Angeles, California.

Question: Who formed this with him
Self-contained rewrite: Who formed Thirty Seconds to Mars with Jared Leto?