What aliens are there in world?

The concept of aliens encompasses a wide range of hypothetical extraterrestrial life forms, from microbial organisms to advanced civilizations. In popular culture, aliens are often depicted as humanoid beings, such as the Greys or Reptilians, but scientific searches, like those conducted by SETI, focus on the possibility of life beyond Earth based on microbial life or intelligent civilizations. However, as of now, there is no conclusive evidence of aliens existing, and they remain a subject of speculation and imagination.