As Chaos Lord is not available for pictures, this is a chaos seed
The Chaos Lord is an entity of apparently great power. He's most likely either some sort of god, demon, or eldritch abomination. Though referred to as 'he', the entity is most likely genderless.
The Chaos Lord's true appearance is unknown. Whenever he makes his wishes known he 'speaks' to his followers with no avatar. The closest anyone has to a guess of what he looks like is the palatial structure which makes up the plane where his followers who choose not to travel their native planes between tasks may choose to dwell. Some theorize the plane literally is his body.
He affects the world via fragments of his soul known as chaos seeds that infect a host. Once infected he can send the host suggestions. How well they resist depends on their own force of will and inclinations.
The seeds grant great powers that their hosts would not otherwise possess, as well as immortality, unless they're killed by someone who knows how to remove the seed. Occasionally, when a host greatly displeases the Chaos Lord, he'll rip the seed out and shove it in a more interesting mortal. Often this kills the host, or drives them even more mad than before.
Many willingly seek his favor as the great power and immortality in exchange for occasionally having to do the bidding of their master seems like an easy deal. He is generally quite willing to grant these; however, the presence of his soul fragments even in a willing host tend to drive them quite bonkers. The weak-willed simply don't survive.
He seems to have a set of definite goals, but they seem to be inscrutable to mere mortals.