The "blame" command:

Usage: fossil annotate|blame|praise ?OPTIONS? FILENAME

Output the text of a file with markings to show when each line of the file
was last modified.  The version currently checked out is shown by default.
Other versions may be specified using the -r option.  The "annotate" command
shows line numbers and omits the username.  The "blame" and "praise" commands
show the user who made each check-in.

Reverse Annotations:  Normally, these commands look at versions of
FILENAME moving backwards in time back toward the root check-in, and
thus the output shows the most recent change to each line.  However,
if the -o|--origin option is used to specify some future check-in
(example: "-o trunk") then these commands show changes moving towards
that alternative origin.  Thus using "-o trunk" on an historical version
of the file shows the first time each line in the file was been changed
by subsequent check-ins.

Options:
  --filevers                  Show file version numbers rather than
                              check-in versions
  -r|--revision VERSION       The specific check-in containing the file
  -l|--log                    List all versions analyzed
  -n|--limit LIMIT            Limit the amount of analysis:
                                N      Up to N versions
                                Xs     As much as possible in X seconds
                                none   No limit
  -o|--origin VERSION         The origin check-in. By default this is the
                                root of the repository. Set to "trunk" or
                                similar for a reverse annotation.
  -w|--ignore-all-space       Ignore white space when comparing lines
  -Z|--ignore-trailing-space  Ignore whitespace at line end

See also: info, finfo, timeline