| Former (14) |
| Unofficial title | 2010 – 2014 |
| Unofficial title | 2006 – 2010 |
| Chief Executive Officer | 2004 – 2008 |
| Chief Executive Officer | 2001 – 2003 |
| Chief Executive Officer | 1992 – 1994 |
| Unofficial title | 1994 – 1998 |
| Chief Executive Officer | 1979 – 1992 |
| Chief Executive Officer | 2014 – 2015 |
| Unofficial title | 1998 – 2002 |
| Unofficial title | 1994 – 1998 |
| Chief Executive Officer | 2003 – 2004 |
| Unofficial title | 1998 – 2002 |
| Chief Executive Officer | 2011 – 2013 |
| Chief Executive Officer | 2008 – 2011 |