Ho eyo he hum

 Ho eyo he hum is a tune commonly sung in the city of Britain. In Ultima I and Ultima III, Iolo sings the tune. In Ultima IV, a small child also happily sings 'ho eyo he hum'.

In Ultima III, Gwino (most likely Gwenno), near Iolo, sings this song backwards, "Muh eh oye oh!".

Ultima V: Lazarus
In the remake of Ultima V, Ultima V: Lazarus, Iolo's response to some commands is to sing this song.