Rubens offers a memorable Silenus (thanks Arline) - more later -
The original Silenus resembled a folklore man of the forest with the ears of a horse and sometimes also the tail and legs of a horse. The later Sileni were drunken followers of Dionysus, usually bald and fat with thick lips and squat noses, and having the legs of a human. Later still, the plural "Sileni" went out of use and the only references were to one individual named Silenus, the teacher and faithful companion of the wine-god Dionysus.
A notorious consumer of wine, he was usually drunk and had to be supported by satyrs or carried by a donkey. Silenus was described as the oldest, wisest and most drunken of the followers of Dionysus, and was said in Orphic hymns to be the young god's tutor. This puts him in a company of phallic or half-animal tutors of the gods, a group that includes Priapus, Hermaphroditus, Cedalion and Chiron, but also includes Pallas, the tutor of Athena.
When intoxicated, Silenus was said to possess special knowledge and the power of prophecy. The Phrygian King Midas was eager to learn from Silenus and caught the old man by lacing a fountain from which Silenus often drank. As Silenus fell asleep, the king's servants seized and took him to their master.