In Ultima series, the player's very own character's title.
There's some clashing information in the canon Ultima games who the Avatar actually is. The introduction of Ultima IV clearly implies that Avatar is just some random guy from the Earth and has no idea about the previous games. However, later parts of the series imply that the Stranger from the stats (the player in the previous three games) and the Avatar are, in fact, the same person. Which is pretty unusual because U1-3 also had non-Human races...
The Avatar lives on Earth, and apparently has fairly normal ways of spending free time, as can be seen in the intros to Ultima VI, Ultima VII, and Ultima IX (aside of the fact that the Avatar isn't even supposed to be on Earth in the beginning of U9)... and gets to the world of Britannia through moongates that appear when the world needs their hero again.
The Avatar, by appearance, is customizable so the character more or less looks like what you look like - this in the games that had good enough graphics to represent it, that is, Ultima VI, VII and SI, and Ultima Underworld 1 and 2. Basically, you can choose the sex and hair color. (In previous parts, you could only choose the sex.)
In the games, the style of Avatar's character is always the same: Usually chain mail (you can, of course, pick other armoring) with white coat over it, with yellow Ankh symbol on front and back. I think he got this cool outfit after truly becoming the Avatar, embodiment of the Eight Virtues, after Ultima IV...
However, this changed in Ultima VIII. In the game, Avatar was always male (IIRC also black-haired). This didn't matter much because you was always in armor and had a fully closed helmet, so Mario Avatar was not "emotionally attachable". This was one of the reasons why U8 wasn't that hot.
In Ultima IX, Origin used what's often affectionately called "Aryan Avatar" (white blond male). In this game, it was not possible to choose the sex or hair color either, even when the game was, according to those who played it, just a tiny bit bit better Ultima-wise than U8.