Harald Welte is a data communications freelancer, enthusiast and hacker who is working with Free Software (and particularly GNU/Linux) since 1995 His major code contribution to the Linux kernel was as a core developer of the netfilter/iptables packet filter.

He has co-started a number of other Free Software and Free Hardware projects, mainly related to RFID such as librfid, OpenMRTD, OpenBeacon, OpenPCD, OpenPICC. During 2006 and 2007 Harald became the co-founder of OpenMoko, where he served as Lead System Architect for the worlds first 100% Open Free Software based mobile phone.

Aside from his technical contributions, Harald has been pioneering the legal enforcement of the GNU GPL license as part of his gpl-violations.org project. More than 150 inappropriate use of GPL licensed code by commercial companies have been resolved as part of this effort, both in court and out of court. He has received the 2007 ""FSF Award for the Advancement of Free Software"" and the ""2008 Google/O'Reilly Open Source award: Defender of Rights"".

In 2008, Harald started to work on Free Software on the GSM protocol side, both for passive sniffing and protocol analysis, as well as an actual network-side GSM stack implementation called OpenBSC. In 2010, he expanded those efforts by creating OsmocomBB, a GSM telephony-side baseband processor firmware and protocol stack. Other projects include OsmocomTETRA, a receive-only implementation of the ETSI TETRA radio interface.

Together with fellow developer Dieter Spaar, Harald has been giving many incarnations of deeply technical trainings about mobile communications protocols from the air inteface to the core network, with a special emphasis on security.

Harald is co-founder of sysmocom GmbH, Berlin/Germany based company working on innovative Free Software based products and solutions for conventional and unconventional operators of mobile networks. Said projects are also used by various entities in research of mobile security.