The general secretary of Wales's first teacher trade union is to step down after less than 18 months in post.
Moelwen Gwyndaf will quit as leader of UCAC, the Welsh-medium teachers'
union, on June 17, to work for the National Library of Wales in Aberystwyth.
The 53-year-old mother of four is leaving for family reasons. Her new post, as a development manager, offers more flexible working hours "on the doorstep" -and a relief from the long hours and travel involved in leading a union.
Colleagues said she would be greatly missed, and in a short period of time had improved how the 4,000-member organisation works. Gruff Hughes, deputy general secretary, will be acting up until elections are held for a successor in September.
He said: "Moelwen's job was 24 hours, seven days a week. We are saddened by her announcement but realise that she has other commitments.
"Moelwen worked very hard in a demanding and difficult role."
Mr Hughes is considering standing as general secretary but said: "I have retirement in my sights as well."
UCAC was the first trade union established in Wales to serve the needs of Welsh teachers, in December 1940.
Ms Gwyndaf, a former primary and secondary school teacher, is known as an "English teacher in Welsh Wales". Welsh is her first language, but she studied English at Bangor university after spending part of her childhood in England. She started her teaching career at Newquay primary school, in west Wales. After taking a career break to bring up her four children, she became an English and drama teacher in the secondary sector.
In the 1960s and 1970s, she took part in Welsh-language protests and describes herself as a political animal. Her move to UCAC five years ago was a natural progression, given her "great love of all things Welsh", she says.
One of only two women to hold high-profile jobs in Welsh classroom teacher unions (the other is Dr Heledd Hayes, education officer at the National Union of Teachers Cymru), she believes class sizes, pupil discipline and rural school closures are the big issues facing teachers now.
Ms Gwyndaf praised the Assembly government for the introduction of the play-based foundation phase for three to seven-year-olds, calling it "extremely exciting". Recently-announced plans to allow teachers three-month career breaks to learn Welsh are also an important move forward, she added.
NUT Cymru spokesman Rhys Williams said: "Moelwen has a great deal of respect in a role which has been traditionally male-dominated in Wales.
"As a union, we share some common ground with UCAC by not voting for the workload agreement, and we applaud Moelwen for her conviction, sincerity and passion."