By Andrew Black
Political reporter, BBC Scotland news website
Whatever you may think of Robin Harper - veteran political visionary or bumbling-yet-endearing parliamentarian - he will be remembered as one of Holyrood's most enigmatic characters.
A shining example of the PR voting system which aimed to create more of a rainbow parliament after devolution in 1999, Mr Harper swept into Holyrood on the Lothian list.
His fedora hat and long, multi-coloured scarf instantly led to comparisons with the eccentric Doctor Who, as portrayed by Tom Baker.
But this was the start of a tenure which would see the former teacher help the Scottish Greens to more success than they thought possible.
Born in Thurso, Caithness, in 1940, Mr Harper's campaign to get green issues on the agenda started long before life as an elected politician.
After a spell teaching English in Kenya and modern studies at Edinburgh's Boroughmuir school, he became the UK's first Green parliamentarian with a tearful acceptance speech on election night in 1999.
He was quickly dubbed one of the "three amigos", along with Socialist Tommy Sheridan and firebrand independent Dennis Canavan, after they resisted attempts to move them to the back of the Holyrood chamber.
Over the next four years, the keen musician single-handedly pressed the Scottish Government on Scottish Green issues, demanding the destruction of GM crops and taking part in anti-nuclear demonstrations.
Robin Harper may not have had a reputation as the most skilled Holyrood debater or political operator, but fact that he served alongside 15 Scottish party leaders is testament to his unwavering popularity
Mr Harper once vowed to "keep a beady eye" on former first minister Jack McConnell's record on environmental issues when overseas, while his popularity also led to stints as rector of both Edinburgh and Aberdeen universities.
Then came the party's greatest moment - the 2003 Scottish election - when the number of Green MSPs ballooned from one to seven.
Mr Harper, always seen as "Scottish Green leader" even though no such position has ever existed, took on a co-leadership role along with Shona Baird, under the party's equal rights policy.
Things did not go so well at the 2007 election, when the fight for votes between Labour and the SNP saw the number of Scottish Green MSPs slashed back to two.
Despite the new, leaner parliamentary party, the Greens saw a chance to make an impact in the new-look Holyrood landscape where the numbers were tight and and SNP minority rule looked likely.
The Greens eventually struck a working deal with the SNP winning the election, but the move was a looser agreement than the one first floated, after the Greens expressed concern about the Nationalist transport policy.
But it ensured the Greens voted for SNP leader Alex Salmond as first minister and support his appointments.
Back in the Holyrood chamber, the only other Green MSP, Patrick Harvie, took on more of the main speaking duties and, despite their small numbers, managed to push the SNP into boosting climate change funding in its first Scottish budget.
After almost 10 years of elected life, Mr Harper decided to call it a day, announcing his decision to step down as co-leader and as an MSP.
He called for the party to consider opting for a single leader - opening the door for the ambitious and capable Mr Harvie to take the reins as the only obvious successor.
Mr Harper may not have had a reputation as the most skilled Holyrood debater or political operator, but fact that he served alongside 15 Scottish party leaders - outlasting 11 of them - is testament to his unwavering popularity and status as a constant force, amid a Scottish Parliament which has seen massive change since 1999.