He rarely deigns to show himself - indeed, his interactions with Perseus indicate he considers knowledge of the Users to be anathema.
His goals are unknown - though theories have been thrown around that he desires the eradication of all knowledge of the Users.
He does not know Poe's true origins - all he is aware of is that being's awareness of User MK's situation - as a result, he has sent Prime, the embodiment of his will, to destroy Poe.
During Ascension, it was revealed that LM was actually collecting Users to put in stasis, and that he was behind Malygos's rise in power. His plan was to have Malygos use his newfound power to blast the User World back into their home dimension, so that the Users' secrets and indeed lives could never be taken by their own characters. User Kon was the last to discover this plan, and considered helping LM, but BBB arrived and kicked LM into his own stasis chamber before he could. Now frozen inside his own palace, it is unknown when the seal is due to break - possibly thousands of years from now.