This works (no regexes necessary):

#!/usr/bin/perl
use strict;
use warnings;

my %first;
while ( <DATA> ) {
    chomp;
    my ($fn,$ln) = split;
    push @{$first{$fn}}, $ln;
}
for my $fn ( keys %first ) {
    my @ln = @{$first{$fn}};
    if ( @ln == 1 ) {
        print $fn,' ',$ln[0],"\n";
    }
    else {
        my $c = 1;
        print $fn,$c++,' ',$_,"\n" for @ln;
    }
}

__DATA__
George Fortran
Jessi Heavens
Bill Clinton
Barack Obama
Bill Gates
Steve Jobs
Bill Green
George Bush
[download]

This doesn't preserve the ordering, though.