AI's glyph - it just provides symbols to you.

glyph  (glf)

n.

1. Architecture A vertical groove, especially in a Doric column or frieze.

2. A symbolic figure that is usually engraved or incised.

3. A symbol, such as a stylized figure or arrow on a public sign, that imparts information nonverbally.

Here, Glyths for Adobe Illustrator. If you want to type theta in, you need to double click theta in the Glyths platte.