What syntax for global 'chown' fix?

[joe at actionline.com]

While the example commands below work to change permission for either a
complete system or for a complete directory and all sub-directories, what
would the syntax be for a similar command to 'chown' (change the owner)
globally or for a designated directory and and the files and
subdirectories below it?

find . -type f -print0 | xargs -0 chmod 644
find . -type d -print0 | xargs -0 chmod 755

find dir -type f -print0 | xargs -0 chmod 644
find dir -type d -print0 | xargs -0 chmod 744