Whether they made lessons fun, ignited your passion for learning or helped you through a difficult time, that person was a big part of your childhood you will never forget.
This retro photo gallery shows much-loved teachers at schools around Northern Ireland with their pupils during the noughties.
Perhaps your favourite teacher is among them, or maybe you will spot an old school friend.
What are your happiest memories of your school days? Let us know in the comments section.
25. Bronte Primary School
P1 teacher Mrs Dianne Toal pictured in the reading corner at Bronte Primary School in 2007 with pupils Euniece Copes, Sarah Mitchell, Rachel Cummings, Rachel Megaw and Rebecca Davidson | National World Photo: Michael Cousins
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26. Tannaghmore Primary School
Teacher Ciara McGovern pictured in 2008 at Tannaghmore Primary School pupils Hannah Magee and Niamh McCann | National World Photo: Geoffrey Cousins