Former Vice President Atiku Abubakar has described former President Goodluck Jonathan as the "face of democracy in Africa".
Mr. Abubakar, a member of the ruling All Progressives Congress, said Mr. Jonathan's democratic ideals were evident in his respect for the will of the people.
Mr. Jonathan turned 60 on Monday. Mr. Abubakar posted a tweet to wish him a happy birthday on Monday morning.
"A very happy 60th birthday to Dr. Goodluck Jonathan @GEJonathan, the Face of Democracy in Africa. Your words that your ambition isn't worth the blood of our citizens will stand forever," the tweet read. "I wish you continued good health and wisdom."
While gearing up for his re-election bid, Mr. Jonathan told Nigerians in 2014 to eschew political violence, saying his ambition was not worth dying for.
He was also hailed for conceding early defeat during the 2015 election, an act his supporters say saved the country from potential post-election violence.
The two leaders were members of the now-opposition Peoples Democratic Party before Mr. Abubakar decamped in 2013 to then recently-formed APC, after attempts to prevail on Mr. Jonathan not to seek a second term failed.
Mr. Abubakar also led many political bigwigs out of the PDP, a development that significantly affected the party's fortunes and culminated in Mr. Jonathan's defeat in 2015.
As 2019 elections draw closer, there are speculations Mr. Abubakar may leave the APC if President Buhari seeks the party's ticket.
Although he has repeatedly shown interest in 2019 run, Mr. Abubakar has been quiet about the platform he plans to pursue his ambition, especially if Mr. Buhari runs as widely feared.
Calls for the former vice-president to return to the PDP have increased of late, with Mr. Jonathan saying last week that the best platform for him to realise his ambition is the PDP.