中国英语界有个流行弊病，以为the only person/man/woman/one 之后的定语从句要用 that 引导，不可以用 who/whom 引导。实际上，用 who/whom 引导不但正确，还远远比that多。

google books http://books.google.com/ 的结果：

the only person who : the only person that    12100,000 : 773,000

the only man who    : the only man that       5650,000  : 741,000

英国语料库http://corpus.byu.edu/bnc/：

the only person who/that       108:19

美国当代语料库http://corpus.byu.edu/coca/：

the only person who/that       510:154

请看最权威的工具书：

柯林斯高级英语用法词典（COLLINS COBUILD DICTIONARY OF ENGLISH USAGE):

The only people who will be killed are those who have knowledge which is dangerous to our cause.

朗文口笔语语法 （LONGMAN GRAMMAR OF SPOKEN AND WRITTEN ENGLISH）:

I'll press-gang some helpers for you, but I do want you there, Wheeler, since
you're the only one who knows what's what.

Sir Alec Guinness is probably the world's best known actor, yet he claims to
be the only one who can walk down a street unrecognised.

"Konrad Schneider is the only one who matters," Reinhold had answered.

CAMBRIDGE ADVANCED GRAMMAR IN USE:

The only people who are interested in the book _____ to be lawyers, (seem)

2 The zoo is the only one in the country where you can see polar bears.

8 _______ for the break-up of the country, he is now the only person who can prevent war.

I recognised Joan easily. She was the only woman (who was) wearing a red and green
hat. (or woman who wore)

我在以上书中没有读到一个句子the only man/woman/person/one + that从句。但有一个是the only things or people that...