The missing character is $\boxed{\text{Q}}$.
The other three characters, $\text{A}$, $\text{F}$, and $\text{R}$, are all in the set of letters that appear in the alphabet twice. The letter $\text{Q}$ is the only letter in the alphabet that does not appear twice.
Here is a table showing the number of times each letter appears in the alphabet:
Letter | Number of times it appears in the alphabet ------- | -------- A | 2 B | 2 C | 2 D | 2 E | 3 F | 2 G | 2 H | 2 I | 3 J | 1 K | 2 L | 2 M | 2 N | 2 O | 2 P | 2 Q | 1 R | 2 S | 2 T | 2 U | 2 V | 2 W | 2 X | 1 Y | 2 Z | 1