Charles has an APT repository for Debian-based Linux distributions.
First install the GPG public key for the repository so you can verify that the packages are correctly signed:
wget -q -O - http://www.charlesproxy.com/packages/apt/PublicKey | sudo apt-key add -
Then add the repository to your sources:
cat > /etc/apt/sources.list.d/charles.list <<EOF
deb http://www.charlesproxy.com/packages/apt/ charles-proxy main
Then update your sources and install Charles:
sudo apt-get update sudo apt-get install charles-proxy
The package creates a "charles" command in /usr/bin, and adds Charles in your application menus in your window manager.
You may also install the beta track of Charles which is called charles-proxy-beta.