The missing character is $\boxed{\text{C}}$.
The sequence is a simple alternating repetition of the letters $A$, $B$, $C$, $D$, $E$, $F$, $G$, $H$, $I$, $J$, $K$, $L$, $M$, $N$, $O$, $P$, $Q$, $R$, $S$, $T$, $U$, $V$, $W$, $X$, $Y$, and $Z$. The first letter is $A$, the second letter is $B$, the third letter is $C$, and so on. The missing letter is the third letter in the sequence, which is $\boxed{\text{C}}$.
Each option is a letter in the alphabet. Option A is the letter $B$. Option B is the letter $C$. Option C is the letter $F$. Option D is the letter $H$.
Option A is not the correct answer because it is not the third letter in the sequence. Option B is the correct answer because it is the third letter in the sequence. Option C is not the correct answer because it is not the third letter in the sequence. Option D is not the correct answer because it is not the third letter in the sequence.